Method and system for binary flow turbine control

ABSTRACT

Methods and systems are provided for adjusting the opening of a scroll valve of a binary flow turbine. Scroll valve adjustments are used at different engine operating conditions to improve engine performance and boost response. Scroll valve adjustments are coordinated with wastegate and EGR valve adjustments for improved engine control.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Patent Application No.61/833,377, filed on Jun. 10, 2013, the entire contents of which arehereby incorporated by reference for all purposes.

FIELD

The present application relates to controlling a scroll valve coupled toa binary flow turbine in a boosted engine system.

BACKGROUND AND SUMMARY

In vehicles having internal combustion engines, it can be beneficial todiscontinue fuel injection to all or some of the engine cylinders duringcertain operating conditions, such as during vehicle deceleration orbraking. For example, one or more cylinder fuel injectors may beselectively deactivated while the engine is rotating. Such an operationis also known as a deceleration fuel shut-off (DFSO) event. The largerthe number of cylinders that are deactivated, and/or the longer thecylinders are deactivated, the greater the fuel economy improvement thatcan be achieved.

However, there may be poor drivability issues during an enginereactivation following the DFSO. As such, following fuel deactivation,the engine may start spinning towards rest. In addition, where theengine is turbocharged, the turbine may also start spinning towardsrest. If a vehicle operator tips-in during the engine spin-down, thetime taken to spool up the turbine may be substantial, and the operatortorque demand may not be timely met. As such, this may degrade engineperformance and vehicle driveability. In addition, while the enginespins down, air may continue to flow through the cylinders towards anexhaust catalyst causing catalyst cooling as well as oxidizing catalyticsites. When combustion is re-initiated, additional fuel may be requiredto reduce and reactivate the exhaust catalyst. During some conditions,this fuel penalty may even outweigh the fuel economy benefits of theDFSO.

The inventors herein have recognized that such drivability issues may beovercome in a boosted engine system that uses a binary flow turbine. Inone example, engine performance may be improved by a method comprisingadjusting a scroll valve coupled to an inlet of one scroll of amulti-scroll exhaust turbine responsive to an indication of enginedeactivation. By closing the scroll valve during a DFSO, turbine speedcan be maintained elevated for a duration, enabling faster turbinespool-up upon subsequent engine reactivation, and reducing catalystcooling.

In one example, in response to a DFSO event, a scroll valve coupled toonly an outer scroll of a multi-scroll exhaust turbine may be moved to amore closed position. For example, the scroll valve may be moved,gradually or immediately, to a fully closed position. The moving of thescroll valve may be based on the turbine speed so that the turbine speedfollows a desired deceleration profile. The scroll valve may then bemaintained at the closed (e.g., fully closed) position during asubsequent engine restart. As such, by closing the scroll valve, theexhaust manifold pressure can be increased, allowing the turbine to keepspinning at or above a threshold speed while the engine spins towardsrest. By enabling the turbine speed to follow a desired speed profile,in response to a sudden request for torque, such as due to a tip-induring the engine spin-down, the turbine may be quickly spooled up andthe boost levels can be elevated. This allows drivability issues duringa DFSO to be reduced. In addition, by closing the scroll valve, theelevated exhaust manifold pressure may reduce fresh air flow through theengine, decreasing the extent of exhaust catalyst cooling and oxidation.As such, this also lowers the fuel penalty required for reducing theexhaust catalyst upon engine reactivation. Wastegate and EGR valveadjustments may be coordinated with the scroll valve adjustments tofurther improve turbine speed control.

In this way, scroll valve adjustments in a binary flow turbine can beadvantageously used to improve turbine speed control during an enginedeactivation as well as during the subsequent engine reactivation. Byimproving turbine speed control, boost performance of the engine duringthe reactivation is improved. In addition, losses in exhaust catalystperformance during the DFSO, due to catalyst cooling and oxidation, arelowered. Overall, engine performance and fuel economy is improved.

It should be understood that the summary above is provided to introducein simplified form a selection of concepts that are further described inthe detailed description. It is not meant to identify key or essentialfeatures of the claimed subject matter, the scope of which is defineduniquely by the claims that follow the detailed description.Furthermore, the claimed subject matter is not limited toimplementations that solve any disadvantages noted above or in any partof this disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic diagram of a boosted engine system including abinary flow turbine and an exhaust gas recirculation (EGR) system.

FIGS. 2-3 show example maps of engine operating conditions that may beused to determine when to transition the binary flow turbine of FIG. 1between one scroll or two scroll configurations.

FIG. 4 shows a map depicting differences in transient torque responsewhen operating the binary flow turbine of FIG. 1 with one or twoscrolls.

FIGS. 5-11 depict example flowcharts for adjusting the position of ascroll valve based on various engine operating conditions.

FIGS. 12-17 depict example scroll valve adjustments commanded responsiveto various engine operating conditions to improve engine performance andboost response.

DETAILED DESCRIPTION

The following description relates to systems and methods for operating aboosted engine including a binary flow turbine and an exhaust gasrecirculation (EGR) system, as shown in FIG. 1. A controller may beconfigured to perform a routine, such as the routine of FIG. 5, toadjust a position of a scroll valve of the turbine (such as from aninitial position) based on various engine operating conditions.Selection of an initial scroll valve schedule may be based on enginespeed-load maps such as those shown at FIGS. 2-3. For example, thescroll valve position may be adjusted during engine starts (FIG. 6) toreduce engine start emissions and turbocharger whine. The valve positionmay be adjusted during torque transients (FIG. 7), such as a tip-in, toreduce turbo lag. The valve position may also be adjusted responsive tocombustion stability limits (FIG. 8), abnormal combustion events (FIG.9), and engine deactivation (FIG. 10). Various engine actuators may beadjusted based on the scroll valve adjustment, such as a turbinewastegate, VCT, spark, EGR valves, etc. For example, as elaborated atFIG. 11, torque disturbances associated with the scroll valve transitionmay be compensated for using concomitant adjustments to one or moreengine actuators. The scroll valve adjustments may improve boostresponse (FIG. 4). Example scroll valve adjustments are described withreference to FIGS. 12-17. In this way, the horsepower capability of aturbocharged engine, and overall engine performance, can be improvedduring various engine operating conditions.

FIG. 1 shows a schematic diagram of an engine 10, which may be includedin a propulsion system of an automobile. Engine 10 may be controlled atleast partially by a control system including controller 12 and by inputfrom a vehicle operator 14 via an input device 16. In this example,input device 16 includes an accelerator pedal and a pedal positionsensor 18 for generating a proportional pedal position signal PP.

Engine 10 may include a plurality of combustion chambers (i.e.,cylinders). In the example shown in FIG. 1, Engine 10 includescombustion chambers 20, 22, 24, and 26, arranged in an inline-4configuration. It should be understood, however, that though FIG. 1shows four cylinders, engine 10 may include any number of cylinders inany configuration, e.g., V-6, I-6, V-12, opposed 4, etc.

Though not shown in FIG. 1, each combustion chamber (i.e., cylinder) ofengine 10 may include combustion chamber walls with a piston positionedtherein. The pistons may be coupled to a crankshaft so thatreciprocating motions of the pistons are translated into rotationalmotion of the crankshaft. The crankshaft may be coupled to at least onedrive wheel of a vehicle via an intermediate transmission system, forexample. Further, a starter motor may be coupled to the crankshaft via aflywheel to enable a starting operation of engine 10.

Each combustion chamber may receive intake air from an intake manifold28 via an air intake passage 30. Intake manifold 28 may be coupled tothe combustion chambers via intake ports. For example, intake manifold28 is shown in FIG. 1 coupled to cylinders 20, 22, 24, and 26 via intakeports 32, 34, 36, and 38 respectively. Each respective intake port maysupply air and/or fuel to the respective cylinder for combustion.

Each combustion chamber may exhaust combustion gases via an exhaust portcoupled thereto. For example, exhaust ports 40, 42, 44 and 46, are shownin FIG. 1 coupled to cylinders 20, 22, 24, 26, respectively. Eachrespective exhaust port may direct exhaust combustion gases from arespective cylinder to an exhaust manifold or exhaust passage.

Each cylinder intake port can selectively communicate with the cylindervia an intake valve. For example, cylinders 20, 22, 24, and 26 are shownin FIG. 1 with intake valves 48, 50, 52, and 54, respectively. Likewise,each cylinder exhaust port can selectively communicate with the cylindervia an exhaust valve. For example, cylinders 20, 22, 24, and 26 areshown in FIG. 1 with exhaust valves 56, 58, 60, and 62, respectively. Insome examples, each combustion chamber may include two or more intakevalves and/or two or more exhaust valves.

Though not shown in FIG. 1, in some examples, each intake and exhaustvalve may be operated by an intake cam and an exhaust cam.Alternatively, one or more of the intake and exhaust valves may beoperated by an electromechanically controlled valve coil and armatureassembly. The position of an intake cam may be determined by an intakecam sensor. The position of exhaust cam may be determined by an exhaustcam sensor.

Intake passage 30 may include a throttle 64 having a throttle plate 66.In this particular example, the position of throttle plate 66 may bevaried by controller 12 via a signal provided to an electric motor oractuator included with throttle 64, a configuration that is commonlyreferred to as electronic throttle control (ETC). In this manner,throttle 64 may be operated to vary the intake air provided thecombustion chambers. The position of throttle plate 66 may be providedto controller 12 by throttle position signal TP from a throttle positionsensor 68. Intake passage 30 may include a mass air flow sensor 70 and amanifold air pressure sensor 72 for providing respective signals MAF andMAP to controller 12.

In FIG. 1, fuel injectors are shown coupled directly to the combustionchambers for injecting fuel directly therein in proportion to a pulsewidth of a signal FPW received from controller 12 via an electronicdriver, for example. For example, fuel injectors 74, 76, 78, and 80 areshown in FIG. 1 coupled to cylinders 20, 22, 24, and 26, respectively.In this manner, the fuel injectors provide what is known as directinjection of fuel into the combustion chamber. Each respective fuelinjector may be mounted in the side of the respective combustion chamberor in the top of the respective combustion chamber, for example. In someexamples, one or more fuel injectors may be arranged in intake passage28 in a configuration that provides what is known as port injection offuel into the intake ports upstream of the respective combustionchambers. Though not shown in FIG. 1, fuel may be delivered to the fuelinjectors by a fuel system including a fuel tank, a fuel pump, a fuelline, and a fuel rail.

The combustion chambers of engine 10 may be operated in a compressionignition mode, with or without an ignition spark. In some examples, adistributorless ignition system (not shown) may provide ignition sparksto spark plugs coupled to the combustion chambers in response tocontroller 12. For example, spark plugs 82, 84, 86, and 88 are shown inFIG. 1 coupled to cylinders 20, 22, 24, and 26, respectively.

Engine 10 may include a turbocharger 90. Turbocharger 90 may include anexhaust turbine 92 and an intake compressor 94 coupled on a common shaft96. The blades of exhaust turbine 92 may be caused to rotate about thecommon shaft as a portion of the exhaust gas stream discharged fromengine 10 impinges upon the blades of the turbine. Intake compressor 94may be coupled to turbine 92 such that compressor 94 may be actuatedwhen the blades of turbine 92 are caused to rotate. When actuated,compressor 94 may then direct pressurized gas to air intake manifold 28from where it may then be directed to engine 10. In this way,turbocharger 90 may be configured for providing a boosted aircharge tothe engine intake.

Turbocharger 90 may be configured as a multi-scroll turbocharger whereinthe exhaust turbine includes a plurality of scrolls. In the depictedembodiment, turbine 92 includes two scrolls including a first outerscroll 95 and a second inner scroll 97. Each scroll may receive exhaustgas from exhaust manifold 29 via distinct inlets. Specifically, exhaustgas may flow along a first exhaust gas entry path 102 into first outerscroll 95 and along a second exhaust gas entry path 104 into secondinner scroll 97. A scroll valve 106 may be coupled in first exhaust gasentry path 102 between engine exhaust manifold 29 and an inlet of thefirst outer scroll 95. In this way, exhaust turbine 92 is configured asa binary flow turbine. As elaborated below, by adjusting a position ofthe scroll valve 106, an amount of exhaust gas directed to the turbinecan be varied. As such, the scroll valve is not coupled to an inlet ofthe second inner scroll.

A wastegate 110 may be coupled across turbine 92. Specifically,wastegate 110 may be included in a bypass 108 coupled between an inletand outlet of the exhaust turbine. By adjusting a position of wastegate110, an amount of boost provided by the turbine may be controlled.

Exhaust gases exiting turbine 92 and/or wastegate 110 may pass throughan emission control device 112. Emission control device 112 can includemultiple catalyst bricks, in one example. In another example, multipleemission control devices, each with multiple bricks, can be used. Insome examples, emission control device 112 may be a three-way typecatalyst. In other examples, emission control device 112 may include oneor more of a diesel oxidation catalyst (DOC), selective catalyticreduction catalyst (SCR), and a diesel particulate filter (DPF). Afterpassing through emission control device 112, exhaust gas may be directedto a tailpipe 114.

Engine 10 may include one or more exhaust gas recirculation (EGR)systems for recirculating an amount of exhaust gas exiting engine 10back to the engine intake. For example, engine 10 may include a first,low pressure EGR (LP-EGR) system 116 for recirculating a portion ofexhaust gas from the exhaust manifold to the intake manifold,specifically, from the engine exhaust, downstream of turbine 92, to theengine intake, upstream of compressor 94. The LP-EGR system may includean LP-EGR conduit 118, an LP-EGR valve 120 configured to control anamount of exhaust gas recirculated along LP-EGR conduit 118, and anLP-EGR cooler 122 for cooling the exhaust gas before delivery to theintake.

Engine 10 may further include a second, high pressure EGR (HP-EGR)system 126 for recirculating a portion of exhaust gas from the exhaustmanifold to the intake manifold, specifically, from the engine exhaust,upstream of turbine 92, to the engine intake, downstream of compressor94. The HP-EGR system may include an HP-EGR conduit 128, an HP-EGR valve130 configured to control an amount of exhaust gas recirculated alongHP-EGR conduit 128, and an HP-EGR cooler 132 for cooling the exhaust gasbefore delivery to the intake.

In some examples, controller 12 may be a conventional microcomputerincluding: a microprocessor unit, input/output ports, read-only memory,random access memory, keep alive memory, and a conventional data bus.Controller 12 is shown in FIG. 1 receiving various signals from sensorscoupled to engine 10, in addition to those signals previously discussed,including: engine coolant temperature (ECT) from a temperature sensor138; an engine position sensor 140, e.g., a Hall effect sensor sensingcrankshaft position. Barometric pressure may also be sensed (sensor notshown) for processing by controller 12. In some examples, engineposition sensor 140 produces a predetermined number of equally spacedpulses every revolution of the crankshaft from which engine speed (RPM)can be determined. Additionally, various sensors may be employed todetermine turbocharger boost pressure. For example, a pressure sensor133 may be disposed in the engine intake downstream of compressor 94 todetermine boost pressure. Additionally, at least the exhaust passagerouting exhaust to outer scroll 95 may include various sensors formonitoring operating conditions of the multi-scroll turbocharger.Exhaust gas sensor 134 may be any suitable sensor for providing anindication of exhaust gas air/fuel ratio such as a linear oxygen sensoror UEGO (universal or wide-range exhaust gas oxygen), a two-state oxygensensor or EGO, a HEGO (heated EGO), a NOx, HC, or CO sensor.

Based on the input from the various sensors, controller 12 may beconfigured to perform various control routines (such as those describedwith reference to FIGS. 5-11) and actuate one or more engine actuators.The actuators may include, for example, intake throttle 64, EGR valves120 and 130, wastegate 110, and scroll valve 106.

As such, by adjusting scroll valve 106 based on engine operatingconditions, the turbine may be operated in different modes, and thedynamic range over which boost can be provided by the turbocharger isenhanced. For example, the turbocharger may be operated in a first modewith the scroll valve closed (e.g., fully closed) during selectedconditions, such as at low engine speeds, during engine cold-starts, andin response to an increased demand for torque. When operating in thefirst mode with the scroll valve closed, the turbine behaves like asmall mono-scroll turbine, providing faster spin-up and BMEP. Herein,the closing of the scroll valve shuts off exhaust flow to the firstscroll. The resulting limited flow of exhaust through only one of thescrolls increases exhaust manifold pressure and turbine inlet pressure(and engine backpressure). By raising the pressure of exhaust flowingthrough the turbine, turbine speed and power in increased, particularlywhen the engine is operating at low speeds and during transientperformance. When coordinated with adjustments to the wastegate, as wellas one or both EGR systems (to provide cooled EGR benefits), the time todesired torque and turbine spin-up can be substantially improved.

As another example, the turbocharger may be operated in a second modewith the scroll valve open (e.g., fully open) during selectedconditions. When operating in the second mode with the scroll valveopen, the turbine behaves like a large mono-scroll turbine, providingimproved peak power. Herein, the opening of the scroll causes exhaust toflow through both the first and second scroll. The resulting drop inexhaust manifold pressure allows more fresh air to be drawn into theengine intake. The increased flow of exhaust through the turbine alsoincreases the driving of the turbine. When coordinated with adjustmentsto the wastegate, as well as one or both EGR systems, boosted engineperformance is improved, a stoichiometric window is enlarged and thefuel economy benefits of cooled EGR are achieved. Example scroll valveadjustments responsive to operating conditions are described withreference to the routines of FIGS. 5-11 and with reference to theexamples of FIGS. 12-17.

While the above modes describe the scroll valve as being either fullyopen or fully closed, it will be appreciated that in still other modes,the scroll valve may be adjusted to any (variable) position between thefully open and fully closed states, based on engine operatingconditions. For example, based on engine operating conditions, thescroll valve may be opened or closed incrementally (e.g., in 20%increments).

Now turning to FIG. 2, map 200 depicts an example scroll valve schedule(and coordination with a wastegate schedule) that may be implemented tooptimize fuel economy and torque production during boosted engineoperation. The map depicts speed-load regions wherein the scroll valvemay be operated closed versus where the scroll valve may be operatedopen. Specifically, map 200 shows engine speed along the x-axis andengine load (as BMEP) along the y-axis.

As shown, when operating in a first region 202, defined by low loadconditions (at low speed as well as at high speed), the engine may beoperated with the scroll valve open as well as the wastegate open. Byopening the scroll valve during the low speed-low load conditions theengine pumping losses can be reduced by reducing the exhaust manifoldpressure.

In comparison, when operating in a second region 204, defined by lowspeed and high load conditions, the engine may be operated with thescroll valve closed. By closing the scroll valve during the high loadconditions, exhaust flow may be restricted to only the inner scroll ofthe turbine. As a result, turbine inlet pressures may be increased,reducing turbo lag and improving low speed transient performance.

During high speed and high load conditions, such as when the engine isoperating in third region 206, the engine may be operated with thescroll valve open and the wastegate partially or fully closed. Byopening the scroll valve while closing the wastegate during the highspeed and high load conditions, a larger portion of exhaust flow may bedirected to both the scrolls to expedite turbine spin-up and boostdelivery. As a result, turbine inlet pressure is reduced, reducingengine backpressure and improving fuel efficiency.

During cold-start conditions, such as when operating in fourth region208, the engine may be started with the scroll valve closed and exhaustflow directed through only one of the scrolls. By closing the scrollvalve during at least an early portion of an engine start operation,catalyst warming to light-off temperatures can be improved.Specifically, by closing the scroll valve during the cold-start, andrestricting exhaust gas flow to be through only one of the multiplescrolls, thermal losses at the turbine (through part of the turbinehousing and a portion of the turbine wheel) are reduced. As such, thisallows a higher exhaust gas temperature to be retained, the higherexhaust gas temperature then directed to the exhaust catalyst.

During the cold-start conditions, the wastegate may be open or closed,depending on the prevalent engine operating conditions, so as tomaximize the temperature of exhaust gas directed to the catalyst and/oroptimize turbo speed for NVH. For example, during an engine cold-startthe engine may be started with the scroll valve closed and the wastegateclosed to increase the temperature of exhaust gas directed to thecatalyst. As another example, during an engine cold-start the engine maybe started with the scroll valve closed and the wastegate open toincrease the temperature of exhaust gas directed to the catalyst byminimizing the heat transfer to the exhaust components. In someembodiments, additional combustion strategies may be implemented withthe scroll valve and wastegate adjustments to reduce time to catalystlight-off. For example, retarded spark ignition timing and valve timingadjustments can be used to complement the reduced exhaust temperaturelosses associated with the closed scroll valve.

Map 300 of FIG. 3 depicts an alternate scroll valve schedule that may beimplemented to optimize fuel economy and torque production duringboosted engine operation. As with the map of FIG. 2, map 300 depictsspeed-load regions (with engine speed shown along the x-axis and engineload (as BMEP) shown along the y-axis) wherein the scroll valve may beoperated closed versus where the scroll valve may be operated open.

In the depicted map, when operating in a first region 302, defined bylow load conditions (at medium to high speeds), the engine may beoperated with the scroll valve open as well as the wastegate open. Byopening the scroll valve and the wastegate during the low loadconditions, exhaust manifold pressure and engine pumping losses areminimized while meeting demanded engine torque.

In comparison, when operating in a second region 304, defined by lowspeed conditions, including low load and high load conditions, theengine may be operated with the scroll valve closed. By closing thescroll valve during the low speed-low load conditions, turbochargertransient response from a low load to a high load condition can beimproved.

For example, during a transient increase in torque demand (e.g., atip-in or a change in speed-load conditions from operating region 302 to304, or from 202 to 204), where the torque request increases beyond acalibratable threshold, the scroll valve may be commanded closed. Thisimproves turbocharger response and results in a faster delivery oftorque. This action may be coordinated with the wastegate, with thewastegate moved towards a closed position when the scroll valve isclosed to further improve turbocharger response. Alternatively, thewastegate may be used to initially manage the residuals (e.g., byinitially being opened) and then be closed to facilitate boostproduction. Further still, the scroll valve and the wastegate may becoupled (electrically or mechanically) such that they close or opentogether.

As with the schedule of FIG. 2, during high speed and high loadconditions, such as when the engine is operating in third region 306,the engine may be operated with the scroll valve open and the wastegatepartially or fully closed. In 302, neither the scroll valve nor thewastegate needs to be closed to meet required boost for engine torquedemand. In region 306, some closing of the wastegate is required to meetdemanded torque but the torque demand can be met with an open scrollvalve. By opening the scroll valve while closing the wastegate duringthe high speed and high load conditions, a larger portion of exhaustflow may be directed to both the scrolls to expedite turbine spin-up andboost delivery while reducing exhaust manifold pressure, residuals andengine pumping losses compared to an open scroll valve. As a result,higher peak power can be achieved.

As engine operating conditions change, a position of the scroll valvemay be adjusted. For example, as engine speed-load conditions change,based on the schedules shown at maps 200 and 300, the scroll valve maybe moved from a fully closed to a fully open position (or vice versa).Further, a wastegate schedule may be coordinated with the scroll valveadjustments. Further still, EGR valve adjustments may be coordinatedwith the scroll valve adjustments to improve cooled EGR delivery.Example adjustments are described herein with reference to FIGS. 12-17.

Now turning to FIG. 4, plot 400 depicts the improvement in transientresponse obtained by moving the scroll valve to a closed position. Plot400 depicts a change in engine torque output (as BMEP) along the y-axis,over time along the x-axis. At t1, a transient increase in torque demandmay be requested, such as due to a tip-in event. In response to thetip-in, turbine operation may be initiated with the scroll valve open(as shown by dashed line 402) or with the scroll valve closed (as shownby solid line 404). Between t1 and t2, while the turbine spins up, theremay be no substantial difference between turbocharger output with thescroll valve open or closed, as this response is dictated by manifoldfilling. However, after t2, the lower engine backpressure experiencedwhen operating with the scroll valve open reduces the transient responseof the turbocharger. In comparison, when operating with the scroll valveclosed, higher torque is achieved, as well as faster attainment of thehigher torque. Further, the closed scroll valve allows for increasedflexibility for trade-offs that may be required during the transientresponse, such as tumble, EGR, etc. If so equipped, an engine withvariable charge motion (tumble) may be used to optimize burn rates foreach condition.

FIG. 5 depicts an example routine 500 that may be performed to adjustthe position of a scroll valve coupled to an outer scroll of amulti-scroll exhaust turbine based on engine operating conditions.Specifically, the routine may determine an initial scroll valve positionand schedule, and then based on engine operating conditions, includingbased on engine limitations, transients, EGR valve limits, etc., theinitial scroll valve position and schedule may be further modified viathe specific routines and sub-routines of FIGS. 6-11. The routine mayfurther enable wastegate adjustments and EGR valve adjustments(including HP-EGR and LP-EGR adjustments) to be coordinated with thescroll valve adjustments to improve engine performance, torque output,and fuel economy.

At 502, the routine includes estimating and/or measuring engineoperating conditions. These may include, for example, engine speed,torque demand, catalyst temperature, engine temperature, exhaustair-fuel ratio, MAP, MAF, barometric pressure, etc. At 504, based on theestimated engine operating conditions, an initial scroll valve positionand schedule may be determined. As used herein, the scroll valveschedule may include determining how and when to transition the scrollvalve to the initial position.

At 506, it may be determined if engine start conditions are present. Forexample, it may be determined if the engine is being started from anengine shutdown condition and/or while an exhaust catalyst is below alight-off temperature. If yes, then at 508, the routine includes furtheradjusting the scroll valve schedule and position (from the initialposition determined at 504) based on the temperature conditions toreduce cold-start emissions, expedite catalyst heating, as well as toreduce the occurrence of any turbocharger whine. As elaborated withreference to FIG. 6, this may include starting the engine with thescroll valve open during some start conditions and starting the enginewith the scroll valve closed during other start conditions. Inparticular, the scroll valve is adjusted to keep the turbocharger speedoutside a resonance zone where turbo whine can occur. Wastegateadjustments may be coordinated with, and based on, the correspondingscroll valve adjustments. Example scroll valve adjustments performedduring engine start conditions are described with reference to FIG. 14.

After an engine start has been completed (hot start or cold start), theroutine proceeds to 514, where it may be determined if there are anytransients. For example, it may be determined if there is a suddenincrease in torque demand (e.g., due to an operator pedal tip-in). Ifyes, then at 516, the routine includes further adjusting a scroll valveschedule and position based on the transient conditions to meet thetransient torque demand and reduce turbo lag. As elaborated withreference to FIG. 7, this may include moving the scroll valve to a moreclosed position in response to an increased torque demand. Wastegateadjustments may be coordinated with, and based on, the correspondingscroll valve adjustments. Example scroll valve adjustments performedduring transient changes in torque demand are described with referenceto FIG. 17.

At 518 (from 514 or 516), it may be determined if the engine iscombustion stability limited. If yes, then at 520, the routine includesfurther adjusting a scroll valve schedule and position based on enginedilution and the combustion stability limits to decrease the amount ofresiduals in the combustion chamber. As elaborated with reference toFIG. 8, this may include moving the scroll valve to a position thatenables less engine dilution to be provided. Wastegate adjustments aswell as EGR valve adjustments (to the HP-EGR valve and/or the LP-EGRvalve) may be coordinated with, and based on, the corresponding scrollvalve adjustments. Example scroll valve adjustments performed duringengine operation where combustion stability is limited are describedwith reference to FIG. 15.

At 522 (from 518 or 520), it may be determined if an engine hardwarelimit has been reached. For example, it may be determined if there isany indication of pre-ignition. If yes, then at 524, the routineincludes further adjusting the scroll valve schedule and position basedon the engine hardware limits to reduce an engine load. As elaboratedwith reference to FIG. 9, this may include moving the scroll valve to amore open position to rapidly reduce an engine load below enginehardware limits. Wastegate adjustments may be coordinated with, andbased on, the corresponding scroll valve adjustments. Furthermore, otherpre-ignition mitigating steps, such as fuel enrichment, may be usedconcurrently with the scroll valve adjustment to further expeditemitigation of the pre-ignition. Example scroll valve adjustmentsperformed in response to an indication of pre-ignition are describedwith reference to FIG. 13.

At 526 (from 522 or 524), it may be determined if engine deactivationconditions have been met. For example, it may be determined if adeceleration fuel shut-off (DFSO) event is being performed. If yes, thenat 528, the routine includes further adjusting the scroll valve scheduleand position based on the engine deceleration indication to reduceturbine speed as per a desired deceleration speed profile and anypotential torque disturbance. As elaborated with reference to FIG. 10,this may include adjusting the scroll valve to a more closed positionbased on turbine speed. Wastegate adjustments, as well as EGR valveadjustments, may be coordinated with, and based on, the correspondingscroll valve adjustments. Example scroll valve adjustments performedduring engine deactivation are described with reference to FIG. 16.

At 530 (from 526 or 528), it may be determined if a torque disturbance(e.g., torque surge or dip) is expected due to the scheduled scrollvalve adjustments (such as due to any of the scheduled scroll valveadjustments at 508-528). If yes, then at 532, the routine includesadjusting one or more engine torque actuators, as well as furtheradjusting a timing of the scroll valve transition (e.g., when the scrollvalve is transitioning to or from an open or a closed position) toreduce the impact of the imminent torque surge/dip. By adjusting thevalve schedule, the torque disturbance may be better masked, improvingthe vehicle operator's drive feel. Further, a timing of the scroll valvetransition may be adjusted to overlap a transmission event. Exampletorque actuator adjustments and scroll valve timing adjustmentsperformed to mask torque disturbances are described with reference toFIG. 12.

In this way, by using scroll valve adjustments, alone or in combinationwith wastegate and EGR valve adjustments, a range of engine operationover which boost benefits can be provided is enhanced. Further, theengine's tolerance to trade-offs performed as operating conditions varyis increased. Overall, engine performance is enhanced while alsoimproving fuel economy.

Now turning to FIG. 6, an example routine 600 that may be performedduring start conditions is described. The routine enables cold-startemissions to be reduced, exhaust catalyst light-off to be expedited andturbocharger speed related NVH issues to be avoided.

At 602, the routine includes estimating and/or measuring engineoperating conditions such as engine coolant temperature, exhaustcatalyst temperature, torque demand, BP, MAP, MAF, etc. In addition, aninitial scroll valve position may be determined based on the estimatedoperating conditions. At 604, the routine includes confirming an enginestart condition. For example an engine start may be confirmed by enginespeed being below a threshold. If engine start conditions are notconfirmed, the routine may end. The engine start may include an enginehot start or an engine cold start. As such, turbocharger NVH concernsmay not necessarily be temperature dependent and may need to be managedregardless of the exhaust catalyst temperature and light off state.

At specific turbocharger rotational speeds in turbocharged enginesystems, NVH issues may occur. For example, a whine can be heard. TheNVH issues may be particularly objectionable during engine starts whenthe overall engine system noise is not sufficient to mask any audibleresonance at the turbocharger. Thus, at 606, it may be determined ifselected engine start conditions are present, for example, startconditions that can lead to objectionable audible resonance at theturbocharger. Specifically, at 606, a turbine speed may be estimated andit may be determined if the turbine speed is within a range R1. In oneexample, the turbine speed range R1 may be based on turbine resonanceand may correspond to a turbine speed range where turbocharger whineduring a start is likely. The threshold range may be based on one ormore manifold pressure, airflow, engine speed, estimated or measuredexhaust gas temperature, and spark timing. In alternate embodiments, theselected start conditions may be further identified based on enginespeed, intake manifold pressure, etc.

If the turbine speed is not inside range R1, the routine proceeds to607, which includes confirming engine cold-start conditions. Forexample, an engine cold-start condition may be confirmed when an exhaustcatalyst temperature is less than a threshold temperature (e.g., acatalyst light-off temperature). As another example, an enginecold-start condition may be confirmed when an exhaust temperature isless than a threshold temperature. As still another example, an enginecold-start condition may be confirmed when the engine has been shut-downfor more than a threshold duration. Further considerations in assessingan engine cold-start condition may include ambient conditions (such asambient temperature conditions), and engine temperature conditions(e.g., based on engine coolant temperature). If engine cold-startconditions are not confirmed, the routine may end.

If cold-start conditions are confirmed, the routine proceeds to 608wherein the engine is started with a scroll valve coupled to an inlet ofone scroll of a multi-scroll exhaust turbine adjusted to expeditecatalyst warm-up. Herein, the one scroll may be a first, outer scroll,the turbine further including a second, inner scroll, the scroll valvenot coupled to an inlet of the second scroll. The adjusting includes, inone example, moving the scroll valve to a more closed position. In oneexample, moving the scroll valve to a more closed position includesmoving the scroll valve to a fully closed position. By closing thescroll valve, the turbine surface area for maximum heat flux to anexhaust catalyst is minimized, expediting catalyst warm-up. In addition,the time required to build boost on a subsequent tip-in is reduced.

The adjusting of the scroll valve may be based on exhaust temperature.For example, when the exhaust temperature at the cold-start is below athreshold, the valve may be moved to a more closed position (e.g., to afully closed position), the valve then moved to a more open position(e.g., towards the fully open position) as the exhaust temperature movesabove the threshold. In the depicted example, the threshold may be anexhaust catalyst light-off temperature. The scroll valve may then bemaintained in the more closed position for a threshold number ofcombustion events since the engine cold-start. Then, after the thresholdnumber of combustion events has elapsed, the scroll valve may be movedto a more open position.

Next, at 610, the routine includes adjusting a turbine wastegateposition based on the scroll valve position to expedite catalystheating. The adjusting includes, as an example, moving the wastegate toa more closed position as the scroll valve is moved to a more closedposition, to pre-position the wastegate to improve boost response onpossible subsequent tip-ins. In some embodiments, the wastegate positionmay be further adjusted based on the exhaust temperature at thecold-start. For example, the wastegate may be moved to a more openposition as the exhaust temperature moves above the threshold. Theroutine may further include adjusting various engine operatingparameters responsive to the scroll valve (and wastegate) adjustment toreduce torque transients during the scroll valve adjustments. Forexample, one or more of spark ignition timing, VCT, EGR and intakethrottle position may be adjusted while moving the scroll valve based onthe scroll valve position.

One or more additional steps may be taken to further expedite exhaustcatalyst heating during the cold-start. For example, at 612, the routineincludes retarding spark ignition timing based on the scroll valveopening. Herein, an amount of spark retard applied may be based on adifference between the exhaust temperature and a light-off temperature.However, by using the scroll valve adjustment, the amount of sparkretard required may be less than the amount required when no scrollvalve adjustment is used. Thus, by reducing the amount of spark retardrequired, fuel economy is improved.

At 614, the routine includes adjusting the scroll valve opening based onthe exhaust temperature. Specifically, as the exhaust temperatureincreases (e.g., above a threshold temperature, such as a light-offtemperature), the scroll valve opening may be increased. That is, as thecatalyst warms up, the scroll valve is gradually moved from the fullyclosed to the fully open position, allowing more exhaust gas to flowthrough both scrolls of the turbine.

Next, at 630, and as further elaborated with reference to FIG. 11, theroutine includes adjusting one or more engine torque actuators, as wellas a timing of the scroll valve transition, to reduce the impact of anytorque surge/dip caused by the scroll valve adjustment. By adjusting theengine torque actuators, any torque disturbance may be better masked,and the vehicle operator's drive feel may be improved. In one example,the adjusting includes adjusting a timing of the scroll valve based on atransmission event to better mask the torque surge.

Returning to 606, if the turbine speed is in range R1, then the routineproceeds to 616 wherein in response to selected engine start conditionsbeing met (wherein the turbine speed is within a threshold range), theengine is started with the scroll valve coupled to the outer scroll ofthe exhaust turbine open. For example, when a cold-start conditionincludes an exhaust catalyst temperature being less than a thresholdtemperature and a turbine speed being below a threshold speed, thescroll valve is adjusted by moving the scroll valve to a more closedposition. In comparison, when the cold-start condition includes theexhaust catalyst temperature being less than the threshold temperatureand the turbine speed being above the threshold speed, the scroll valveis adjusted by moving the scroll valve to a more open position. As such,an opening of the scroll valve may be adjusted based on each of theturbine speed and an exhaust temperature.

While a nominal scroll valve position that is closed is advantageous forexpediting catalyst light-off and reducing time to build boost, duringsome conditions, the closed position of the scroll valve can result in aturbocharger speed that elicits the audible resonance that isobjectionable to the driver and/or passengers of the vehicle. In suchinstances, by commanding the scroll valve to the open position, theturbocharger speed is reduced, thereby moving the turbocharger out ofthe resonance conditions, and mitigating the objectionable noise. Assuch, the conditions at which the scroll valve may be opened may dependon, in addition to catalyst temperature and turbine speed, factors suchas engine speed, air flow, intake manifold pressure, engine coolant orcylinder head temperature, air-fuel ratio, spark retard, torque reserve,exhaust manifold temperature and pressure and other similar parametersthat are indicative of a cold start and which define the energydelivered by the turbine.

At 618, the routine includes adjusting an opening of a wastegate coupledacross the exhaust turbine. Specifically, the controller may increase anopening of the wastegate while an opening of the scroll valve isincreased to further reduce turbocharger speed and improve NVH. An orderof opening of the wastegate and the scroll valve may be based on, forexample, a relative authority of each of the wastegate and the scrollvalve at the given operating conditions. For example, when turbineenergy changes sufficiently, one or the other may be opened initially,while the other is closed. By coordinating the action of the scrollvalve with the action of the wastegate, both the wastegate and thescroll can be used to mitigate the NVH issues that arise as turbineenergy changes. Further, while the depicted example suggests opening thescroll valve and closing the wastegate, in alternate examples, thewastegate may be opened while the scroll valve is closed. One or theother may be closed to pre-position the wastegate to improve boostresponse on possible subsequent tip-ins and/or manage turbo speed forNVH and/or maximize heat flux to the exhaust catalyst.

At 620, it may be determined if the turbine speed is outside range R1.If not, then at 622, the controller may maintain each of the scrollvalve and wastegate open until the turbine speed is outside of thethreshold range. Else, after the turbine speed is outside of thethreshold range, the controller may adjust a position of each of thescroll valve and the wastegate based on exhaust temperature.Specifically, upon confirming that the turbine speed is outside rangeR1, at 624, the routine determines if the exhaust temperature is abovethe catalyst light-off temperature. If yes, then the routine moves to626 wherein the scroll valve is moved to a scheduled position that isbased on engine operating conditions. If not, the routine moves to 628,wherein the scroll valve is moved to a more closed position to expeditecatalyst heating, the scroll valve opening then increased as the exhausttemperature increases and the exhaust catalyst becomes sufficientlywarmed. In other words, the controller maintains each of the scrollvalve and wastegate open until the turbine speed is outside of thethreshold range. Then, after the turbine speed is outside of thethreshold range, a position of each of the scroll valve and thewastegate is adjusted based on exhaust temperature.

From both 626 and 628, the routine proceeds to 630 wherein, aselaborated with reference to FIG. 11, the routine includes adjusting oneor more engine torque actuators to better mask any torque disturbancescaused by the scroll valve adjustment. Specifically, one or more of EGR,VCT, spark timing, and intake throttle position is adjusted during theengine cold-start based at least on the scroll valve adjustment.

It will be appreciated that while the depicted routine is ended inresponse to start conditions not being confirmed, in alternateembodiments, if no scroll valve adjustment is confirmed, an enginehot-start condition may be further confirmed. For example, based onwhether the engine is already sufficiently heated (where one or more ofengine temperature, exhaust temperature, and exhaust catalysttemperature are sufficiently high) or based on the engine beingshut-down for less than a threshold duration, a hot start condition maybe confirmed. During engine hot-start conditions, the scroll valve maybe adjusted to expedite turbine spin-up and/or manage turbo speed forNVH. For example, the engine may be started with the scroll valve movedto a more open position.

It will also be appreciated that while the example of routine 600discusses scroll valve adjustments used to manage turbo whine at lowspeed conditions of engine starts, similar turbo whine may beexperienced at other low engine speed conditions not associated with astart. During such low speed conditions not associated with a start, thescroll valve may be similarly adjusted to a position that removes theturbine from a speed range that produces whine. The scroll valveposition that avoids such a turbine speed may change based on the engineoperating conditions, especially based on air-flow rate, exhaust gaspressure, and wastegate position.

In one example, during a first engine start conditions (e.g., a firstengine cold-start condition), the engine may be started with the scrollvalve open for a first, larger number of combustion events, while duringa second engine start condition (e.g., a second, different engine coldstart condition or an engine hot-start condition), the engine is startedwith the scroll valve more open for a second, smaller number ofcombustion events. The first engine start condition may include anexhaust catalyst temperature being lower than a threshold temperature,while the second engine start condition may include the exhaust catalysttemperature being higher than the threshold temperature. During thefirst engine start condition, an opening of the scroll valve may beadjusted based on the exhaust catalyst temperature while during thesecond engine start condition, the opening of the scroll valve may beadjusted based on the catalyst temperature, as well as turbochargerspeed. The adjusting of the scroll valve during the first engine startmay include, as an example, for a first number of combustion events,starting the engine with the scroll valve moved to a more closedposition (e.g., fully closed) and as the exhaust catalyst temperatureincreases, increasing an opening of the scroll valve. Then, after thefirst number of combustion events, moving the scroll valve to a fullyopen position. In comparison, adjusting of the scroll valve during thesecond engine start may include, as an example, for a second number ofcombustion events, starting the engine with the scroll valve moved to amore open position (e.g., partially closed or fully open) and as theexhaust catalyst temperature increases, increasing an opening of thescroll valve. Then, after the second number of combustion events, movingthe scroll valve to a fully open position. In one example, each of thefirst number and second number of combustion events may be based on anexhaust temperature at engine start. Alternatively, the number ofcombustion events may be based on engine coolant temperature uponstart-up.

Further, during the first engine start condition, the engine may bestarted with a wastegate coupled to the exhaust turbine more open forthe first, number of combustion events while during the second enginestart condition, the engine is started with the wastegate more open fora second number of combustion events. Herein, during each of the firstand second engine start conditions (e.g., cold-start and hot-startconditions), the opening of the wastegate may be based on the opening ofthe scroll valve.

In one example, an engine system comprises an engine, and a turbochargerfor providing a boosted aircharge to the engine, wherein theturbocharger includes an intake compressor and an exhaust turbine. Theexhaust turbine may include a first outer and a second inner scroll, anda scroll valve may be coupled between an engine exhaust manifold and aninlet of the first outer scroll. The engine system may further include awastegate in a bypass coupled between an inlet and an outlet of theturbine. A controller of the engine system may be configured withcomputer readable instructions for, during an engine start (e.g.,cold-start) condition, starting the engine with an opening of the scrollvalve adjusted responsive to exhaust temperature for a number ofcylinder events since a first combustion event. The adjusting mayinclude, starting the engine with the scroll valve more closed, andincreasing an opening of the scroll valve as the exhaust temperaturerises. Alternatively, the controller may be configured with computerreadable instructions for, during an engine start (e.g., hot start orcold-start) condition, where turbine speed is lower than a thresholdspeed, starting the engine with an opening of the scroll valve increasedbased on the turbine speed. Then, after the turbine speed is higher thanthe threshold, decreasing the opening of the scroll valve (e.g., basedon exhaust temperature. The controller may include further instructionsfor adjusting the wastegate while adjusting the scroll valve during thecold-start, the wastegate adjustment based on the scroll valveadjustment to expedite exhaust catalyst heating during the cold-start.

In this way, adjustments to a scroll valve position may be used duringengine start conditions to move turbine speed out a speed range thatproduces turbo whine. Scroll valve position adjustments may also beadvantageously used during the engine start to expedite catalyst heatingand reduce cold-start emissions. An example scroll valve adjustment isnow described with reference to FIG. 14.

Map 1400 of FIG. 14 depicts adjusting of a scroll valve coupled to aninlet of an outer scroll of a multi-scroll exhaust turbine responsive toengine start conditions, specifically, responsive to an enginehot-start, or different engine cold-start conditions. Map 1400 depictsexhaust temperature at plot 1402, scroll valve adjustments at plot 1404,and engine conditions (on or off) at plot 1406. All plots are depictedover time, plotted along the x-axis.

Prior to t1, the engine may be shutdown. At t1, an engine restartrequest may be received. The engine restart at t1 may be an enginecold-start due to the engine being shut-down for a duration that islonger than a threshold. As such, over the duration of the engineshutdown, an exhaust catalyst may have cooled (plot 1402) to below alight-off temperature (Tcat). Thus, at t1, an engine cold-start may beinitiated wherein the engine is spun up. In the depicted example, thecold-start condition at t1 may be a first cold-start condition, wherethe turbine speed is outside a threshold range where turbo whine canoccur. As such, the threshold range may be based on one or more ofmanifold pressure, engine speed, and spark timing. Thus, the firstcold-start condition may include no indication of turbochargerresonance. Accordingly, at t1, the engine may be started (plot 1405)with the scroll valve moved to a more closed position (plot 1404). Inthe depicted example, the scroll valve may be moved to a fully closedposition. By closing the scroll valve, heat loss through the turbine isreduced, increasing the exhaust heat transferred to the exhaustcatalyst. As such, this expedites exhaust warm-up.

The engine may be started with the scroll valve in the more closedposition for a first, larger number of combustion events since theengine start. In the depicted example, the scroll valve is maintainedclosed for a duration between t1 and t2. Then, after the thresholdnumber of combustion events have elapsed, at t2, the scroll valveopening may be adjusted based on the exhaust temperature. In thedepicted example, at t2, the exhaust may also be at the light-offtemperature. Thus, as the exhaust temperature increases above thethreshold temperature after t2, the scroll valve opening may begradually increased until it is fully open. In alternate examples, thescroll valve may be immediately moved to a fully open position. Thenengine may then be operated with the scroll valve fully open. By openingthe scroll valve, engine pumping losses are reduced.

After t2 and before t3, the engine may be shut-down temporarily. Forexample, the engine may be in an idle-stop condition, where the engineis selectively deactivated. The engine deactivation may be short enoughthat the exhaust catalyst is not sufficiently cooled and is at or aboveTcat (plot 1402). At t3, an engine restart request is received. Inresponse to the engine hot-start condition at t3, the engine may berestarted (plot 1406) with the scroll valve open (in the depictedexample, fully open).

After t3 and before t4, the engine may be shut-down. At t4, an enginerestart request may be received. The engine restart at t4 may also be anengine cold-start due to the engine being shut-down for a duration thatis longer than a threshold. As such, over the duration of the engineshutdown, an exhaust catalyst may have cooled (plot 1402) to below alight-off temperature (Tcat). In addition, the scroll valve may beclosed during the shut-down. Thus, at t4, an engine cold-start may beinitiated wherein the engine is spun up. In the depicted example, thecold-start condition at t4 may be a second cold-start condition, wherethe turbine speed is inside a threshold range where turbo whine canoccur. As such, the threshold range may be based on one or more ofmanifold pressure, engine speed, and spark timing. Thus, the secondcold-start condition may include an indication of potential turbochargerresonance. Accordingly, at t4, the engine may be started (plot 1405)with the scroll valve moved to a more open position (plot 1404), such asa fully open position. By opening the scroll valve, exhaust manifoldpressure is reduced, and turbine speed is reduced. This brings theturbine speed out of the range where whine can occur. In the depictedexample, the scroll valve may be moved to a fully open position.

The engine may be started with the scroll valve in the more openposition for a second, smaller number of combustion events since theengine start (as compared to the first number of combustion events atthe first cold start at t1). In the depicted example, the scroll valveis maintained open for a duration between t4 and t5. Then, after thethreshold number of combustion events have elapsed, at t5, the scrollvalve opening may be adjusted based on the exhaust temperature. In thedepicted example, at t5, the exhaust may still be below the light-offtemperature. Thus, after t5, the scroll valve is gradually closed toexpedite catalyst warm-up until the scroll valve is fully closed beforet6. At t6, the exhaust temperature increases above the thresholdtemperature responsive to which the scroll valve opening is increased toa fully open position. Then engine may then be operated with the scrollvalve fully open.

While not depicted in the example of FIG. 14, in further examples, acontroller may adjust a wastegate coupled across the exhaust turbineresponsive to the cold-start or hot start condition. The controller mayalso adjust various engine torque actuators, such as one or more ofspark ignition timing, VCT, and intake throttle position based on thescroll valve adjustment. In this way, by adjusting a scroll valveadjustment during an engine cold-start, catalyst warm-up is expedited,cold-start exhaust emissions and turbo whine are reduced.

Now turning to FIG. 7, an example routine 700 is shown for adjusting ascroll valve coupled to an inlet of an outer scroll of a multi-scrollexhaust turbine responsive to an increased torque demand, such asfollowing a tip-in. The approach allows turbo lag to be reduced.

At 702, the routine includes estimating and/or measuring engineoperating conditions such as engine coolant temperature, exhaustcatalyst temperature, torque demand, BP, MAP, MAF, etc. In addition, aninitial scroll valve position may be determined based on the estimatedoperating conditions.

At 704, a tip-in may be confirmed. For example, it may be determined ifthe torque demand has increased by more than a threshold amount, and/orwhether an accelerator pedal has been depressed by more than a thresholdamount. If tip-in conditions are not confirmed, at 720, the routineincludes moving the scroll valve to the initial position, as determinedand scheduled at 702. Further, at 722, a position of a wastegate coupledacross the exhaust turbine may be adjusted based on the scheduled scrollvalve position so that the engine torque demand estimated at 702 can beprovided. Further still, residuals may be recirculated from the engineexhaust to the engine intake via the EGR system(s), with the valvesadjusted to settings determined at 702, to meet the torque demand. Thisincludes adjusting an LP-EGR valve if the engine system include anLP-EGR system and an HP-EGR valve if the engine system includes anHP-EGR system to provide the determined amount of exhaust gasrecirculation.

If a tip-in is confirmed, then at 706, the routine includes, in responseto the tip-in, adjusting an opening of a scroll valve coupled to theouter scroll of a multi-scroll exhaust turbine to reduce turbo lag.Specifically, the adjusting includes reducing the opening of the scrollvalve. That is, the scroll valve may be moved to a more closed position.In one example, the scroll valve may be moved to a fully closedposition. The scroll valve closing may be based on the torque demandedat the tip-in. For example, the scroll valve closing may be based on adifference between the torque demanded and the torque that can beprovided at the engine operating conditions existing at the tip-in. Asthe difference increases, the scroll valve may be moved closer to afully closed position to improve turbine spin-up. In an alternateexample, the reducing the opening of the scroll valve may be based on anestimated or measured turbine speed at the tip-in. Therein, as adifference between the estimated or measured turbine speed and arequested turbine speed (based on the torque demanded) increases, thescroll valve towards may be moved towards the fully closed position. Instill a further example, the reducing the opening of the scroll valvemay be based on an estimated or measured boost pressure at the tip-in.Therein, as a difference between the estimated or measured boostpressure and a requested boost pressure (based on the torque demanded)increases, the scroll valve towards may be moved towards the fullyclosed position. By closing the scroll valve responsive to the tip-in,exhaust manifold pressure may be increased, thereby expediting turbinespin-up. As such, this reduces turbo lag and allows the increased torquedemand to be quickly met. In some examples, the scroll valve opening mayalso be adjusted based on ambient air density, such as during thetip-in, the valve moved towards a fully closed position as the ambientair density decreases.

At 708, the routine includes, adjusting an opening of a wastegatecoupled across the exhaust turbine in response to the tip-in, thewastegate opening based on the scroll valve opening. By closing thewastegate, exhaust manifold pressure can be further increased. Forexample, the wastegate may be moved towards a fully closed position asthe scroll valve is moved towards the fully closed position. A timing ofthe wastegate adjustment may be based on a timing of the scroll valveadjustment and further based on an authority of the wastegate relativeto the authority of the scroll valve. For example, when the wastegatehas lower authority relative to the scroll valve, the wastegateadjustment may follow the scroll valve adjustment. That is, first thewastegate may be kept open while the scroll valve is moved to the closedposition, and then the scroll valve may be opened while the wastegate isclosed. In another example, when the wastegate has higher authorityrelative to the scroll valve, the wastegate adjustment may lead or beconcurrent with the scroll valve adjustment. That is, first the scrollvalve may be kept open while the wastegate is moved to the closedposition, and then the wastegate may be opened while the scroll valve isclosed. Alternatively, they may be concurrently closed.

At 710, the routine includes adjusting an amount of exhaust gasrecirculated to the engine intake. Specifically, an amount of EGR may bereduced as the scroll valve moves towards the fully closed position. Insome embodiments, the engine may include an EGR system having an LP-EGRvalve in an LP-EGR passage for recirculating exhaust gas from theexhaust manifold, downstream of the turbine, to the intake manifold,upstream of the compressor, as well as an HP-EGR valve in an HP-EGRpassage for recirculating exhaust gas from the exhaust manifold, fromupstream of the turbine, to the intake manifold, downstream of thecompressor. The engine controller may adjust each of the LP-EGR valveand the HP-EGR valve in response to the tip-in to vary a ratio of HP-EGRto LP-EGR based on the scroll valve closing. As one example, thecontroller may increase an opening of the LP-EGR valve while decreasingan opening of the HP-EGR valve to increase a ratio of LP-EGR to HP-EGR.In another example, the controller may decrease the opening of each ofthe LP-EGR valve and the HP-EGR valve to reduce engine dilution.

At 712, it may be confirmed if the elevated torque demand (responsive tothe tip-in) has been met. In one example, it may be determined that thetorque demand has been met if the turbine has sufficiently spun up.Thus, at 712, it may be determined if the turbine speed is above thethreshold. If not, then at 716, the controller may maintain the scrollvalve closed until the turbine speed is at or above the threshold speed(or boost pressure is at or above a requested boost pressure).Alternatively, the controller may continue reducing the opening of thescroll valve (towards the fully closed position), or maintain the scrollvalve at a closed position, until the turbine speed is at or above thethreshold speed (or boost pressure is at or above the requested boostpressure).

At 714, after the turbine speed, or in another example boost pressure,is at or above a threshold, the routine includes opening the scrollvalve. For example, the scroll valve may be fully opened.

At 716, as further elaborated with reference to FIG. 11, the routineincludes adjusting one or more engine torque actuators, as well as atiming of the scroll valve transition, to reduce the impact of anytorque surge/dip caused by the scroll valve adjustment. By adjusting theengine torque actuators, any torque disturbance may be better masked,and the vehicle operator's drive feel may be improved. In one example,the adjusting includes adjusting a timing of the scroll valve based on atransmission event following the tip-in to better mask the torquedisturbance.

In this way, adjustments to a scroll valve during a tip-in may beadvantageously used to expedite turbine spin-up and improve boostperformance during the tip-in. An example scroll valve adjustment is nowdescribed with reference to FIG. 17.

Map 1700 of FIG. 17 depicts adjusting of a scroll valve coupled to aninlet of an outer scroll of a multi-scroll exhaust turbine responsive toincreased torque demand, specifically, responsive to a tip-in. Map 1700depicts an engine torque at plot 1702, turbine speed at plot 1704,scroll valve adjustments at plot 1706, wastegate adjustments at plot1708, HP-EGR valve adjustments at plot 1710, and LP-EGR valveadjustments at plot 1712. All plots are depicted over time, plottedalong the x-axis.

Prior to t1, the engine may be operating with each of the scroll valve(plot 1706) and the wastegate (plot 1708) at least partially open toprovide engine torque (plot 1702) control. At t1, a tip-in event may beconfirmed. In response to the tip-in event, the scroll valve coupled toan outer scroll of a multi-scroll turbine is moved to a more closedposition. In the depicted example, closing the scroll valve includesfully closing the scroll valve. As such, the scroll valve may be keptclosed for a duration following the tip-in until the turbine speed (plot1704) is at or above a threshold speed. In the depicted example, thescroll valve is maintained closed from t1 to t2. At t2, when the turbinespeed is sufficiently high (e.g., above a threshold speed), the scrollvalve is opened. In the depicted example, opening the scroll valveincludes fully opening the scroll valve.

In one example, the duration of scroll valve closing may be based onturbine speed following the tip-in, with the duration increased as theturbine speed following the tip-in decreases. In other words, if alarger spin-up is required, the scroll valve may be moved to a moreclosed position, while if a smaller spin-up is required, the scrollvalve may be moved to a relatively less closed position. By closing thescroll valve responsive to a tip-in, an exhaust manifold pressure can berapidly increased, thereby enabling the turbine to quickly spin-up. Assuch, this reduces turbo lag and allows transients to be betteraddressed. In comparison, if the scroll valve was not closed followingthe tip-in, an amount of time taken to spin up the turbine may belonger, as shown by plot 1703 (dashed line), and as also shown at FIG.4.

At t1, while closing the scroll valve, a net amount of EGR delivered tothe engine may also be reduced. This may include reducing an opening ofan LP-EGR valve coupled to an LP-EGR system, or reducing an opening ofan HP-EGR valve coupled to an HP-EGR system. Further still, thecontroller may adjust the opening of each of the LP-EGR valve and theHP-EGR valve to vary a ratio of LP-EGR to HP-EGR delivered to theengine. In the depicted example, an opening of the HP-EGR valve (plot1710) is decreased to reduce an amount of residuals recirculated fromupstream of the turbine to downstream of the compressor. At the sametime, an opening of the LP-EGR valve (plot 1712) is increased toincrease an amount of residuals recirculated from downstream of theturbine to upstream of the compressor. As such, the net amount of EGRand engine dilution may be reduced. In alternate embodiments, the netamount of EGR may be maintained while the scroll valve is closed.

At t1, to further assist in turbine spin-up, the wastegate is keptclosed responsive to the closing the scroll valve. Herein, the wastegatehas higher, or comparable authority and therefore is adjusted concurrentto the scroll valve. However in alternate examples, such as when thewastegate has lower authority, the wastegate adjustment may follow thescroll valve adjustment. The wastegate may also be controlled tointermediate positions to actively control boost to a desired set point.In some examples, the timing of the scroll valve adjustment may befurther based on a transmission event following the tip-in.

At t3, in response to sufficient turbine and engine spin-up, thewastegate may be opened after the scroll valve is opened. In addition,at t3, an opening of the LP-EGR valve may be reduced while an opening ofthe HP-EGR valve is increased, so as to increase the net amount ofengine dilution. In an alternate example, a controller may open thescroll valve while maintaining the amount of EGR delivered to theengine. In yet another example, the opening of the HP-EGR valve may bereduced while an opening of the LP-EGR valve is increased, so as toincrease the net amount of engine dilution.

While not depicted in the example of FIG. 17, in further examples, acontroller may adjust various engine torque actuators, such as one ormore of spark ignition timing, VCT, valve overlap, and an intakethrottle position based on the scroll valve adjustment, the measuredboost pressure and the torque transients. In this way, scroll valveadjustments may be performed responsive to transient torque demands. Byclosing the scroll valve when torque demand increases, turbine spin upcan be expedited. By adjusting the engine dilution (via EGR valveadjustments) based on the scroll valve adjustment, torque transients andcombustion stability concerns can be better addressed, improving engineperformance.

Now turning to FIG. 8, an example routine 800 is shown for adjusting ascroll valve coupled to an inlet of an outer scroll of a multi-scrollexhaust turbine responsive to engine dilution. The approach allowscombustion stability limits for engine combustion to be improved.

At 802, the routine includes estimating and/or measuring engineoperating conditions such as engine coolant temperature, exhaustcatalyst temperature, torque demand, BP, MAP, MAF, etc. In addition, aninitial scroll valve position may be determined based on the estimatedoperating conditions.

At 804, the routine includes determining an engine dilution requiredbased on the estimated operating conditions. The engine dilution requestmay include a request for LP-EGR and/or a request for HP-EGR. Further,an amount of residuals to be recirculated from the engine exhaustmanifold to the engine intake manifold, such as via an EGR system, maybe determined based on the required dilution and the estimated operatingconditions. As used herein, recirculating via an EGR system may includerecirculating via a low-pressure EGR system coupled between the engineexhaust, downstream of the turbine, and the engine intake, upstream ofan intake compressor, by opening a first EGR valve and/or recirculatingvia a high-pressure EGR system coupled between the engine exhaust,upstream of the turbine, and the engine intake, downstream of the intakecompressor, by opening a second, different EGR valve. Further, residualsmay be recirculated from the engine exhaust to the engine intake via theEGR system(s) to provide the desired dilution until a combustionstability limit is reached

At 806, it may be determined if an engine combustion stability has beenreached, or is being approached. Fuel economy and emissions can beimproved at many engine operating conditions by increasing the amount ofburned gas trapped in a cylinder (also referred to as residuals). Thisburned gas can be introduced during a valve overlap period (internalEGR), or by recirculating exhaust gas to the engine intake (externalEGR). The recirculated exhaust gas can be taken from the exhaust pathupstream (HP-EGR) or downstream (LP-EGR) of the turbine, and may or maynot be cooled. However, there may be limits to the amount of residualsthat can be tolerated due to combustion stability constraints. Forexample, residuals may need to be limited at high load conditions toallow the demanded torque to be delivered. In one example, it may bedetermined at 806 if the engine will operate at or near combustionstability limits when operating with the EGR valves and the scroll valveat the initially scheduled position. Herein, the combustion stabilitylimits may have been previously determined based on the engine operatingconditions and parameters.

If combustion stability limits have not been reached, then at 816, theroutine includes moving the scroll valve to the initial position, asdetermined and scheduled at 802. Further, at 818, a position of awastegate coupled across the exhaust turbine may be adjusted based onthe scheduled scroll valve position and the engine dilution request sothat the required engine dilution can be provided. Further still,residuals may be recirculated from the engine exhaust to the engineintake via the EGR system(s), with the valves adjusted to settingsdetermined at 802, to provide the desired dilution until a combustionstability limit is reached.

If combustion stability limits have been reached, then at 808, theroutine includes, adjusting the scroll valve position responsive to theengine dilution request relative to the engine combustion stabilitylimits. This includes moving the scroll valve to a more closed positionas a request for engine dilution increases, and moving the scroll valvetowards a more open position as a request for engine dilution decreases(to reduce internal residuals). For example, the scroll valve schedulemay be adjusted based on intake manifold pressure. Therein, as themanifold pressure increases (above a threshold pressure), the scrollvalve may be moved towards the more open position.

The scroll valve adjustment may be further based on whether the dilutionrequest was for LP-EGR or HP-EGR. For example, when the dilution requestis for increased HP-EGR, the scroll valve may be moved to a more closedposition to ensure that the exhaust manifold pressure is sufficientlyhigh to flow EGR to the intake manifold (e.g., the exhaust manifoldpressure is higher than the intake manifold pressure). In comparison,when the dilution request is for increased LP-EGR, the scroll valve maybe moved to a more open position.

As such, the position of the scroll valve affects the amount of internalEGR delivered to the cylinders through its impact on the exhaustmanifold pressure during the valve overlap period. Further, for enginesystems configured with LP-EGR, the position of the scroll valve affectsthe maximum turbine energy. This, in turn, dictates the maximum amountof air and/or EGR that can be delivered to the engine system through thecompressor. Further still, for engine systems configured with HP-EGR,the position of the scroll valve affects EGR delivery via its impact onthe exhaust manifold pressure. It also changes the available turbineenergy, thereby also dictating the maximum amount of air that can bedelivered to the engine system through the compressor.

At 810, an intake and/or exhaust valve timing may be adjusted based onthe scroll valve position to adjust an amount of internal EGR deliveredto the engine. For example, where the valve timing is adjusted via avariable cam timing (VCT) device, VCT adjustments may be used todecrease an amount of intake to exhaust valve overlap to decrease anamount of residuals delivered via internal EGR. Valve timing adjustmentsmay include retarding intake valve opening and/or advancing exhaustvalve closing. By opening the intake valve later and/or closing theexhaust valve earlier, while the scroll valve is at the more closedposition, internal EGR is reduced.

At 812, one or more of the LP-EGR valve and the HP-EGR valve may beadjusted based on the scroll valve position to adjust an amount ofexternal EGR delivered to the engine. As one example, while moving thescroll valve to the more closed position, an opening of the first LP-EGRvalve and/or the second HP-EGR valve may be reduced to reduce an amountof residuals delivered to the engine via external EGR. As anotherexample, the controller may maintain the first LP-EGR valve and/or thesecond HP-EGR valve open while decreasing the opening of the scrollvalve. It will be appreciated that while the above routine discussesmaking scroll valve adjustments to meet engine dilution needs when theengine reaches combustion stability limits, in still furtherembodiments, the scroll valve adjustments may be made to meet enginedilution needs when at least one of the LP-EGR valve and the HP-EGRvalve reaches a limit. This may include, for example, an opening limit(beyond which the valve cannot be opened any further) or a closing limit(beyond which the valve cannot be closed any further) of the EGR valves.As such, when any of the EGR valves reach their opening or closinglimit, further changes to residual amounts, as well as a further changein LP-EGR to HP-EGR ratio may be provided by corresponding adjustmentsto the scroll valve. Wastegate adjustments may be concomitantly usedwith, and based on the scroll valve adjustments, to meet the enginedilution requirement.

At 814, the routine includes adjusting one or more engine actuatorsduring the scroll valve transition to reduce any impact of a torquedisturbance resulting from the scroll valve adjustment. For example, theroutine may include adjusting one or more of a wastegate coupled to theexhaust turbine, spark ignition timing, VCT, positive valve overlap, andintake throttle opening while moving the scroll valve to the more closedposition wherein the adjusting is based on each of the scroll valveposition and engine dilution. As elaborated with reference to FIG. 11,the actuator adjustment may be used to better mask any torque surge/dipthat may arise during the scroll valve adjustment, thereby improving thevehicle operator's drive feel. In one example, a timing of the scrollvalve adjustment is based on a transmission event to better mask thetorque disturbance.

In this way, adjustments to the LP-EGR valve and HP-EGR valve can becoordinated with wastegate and scroll valve actions so as to manageresiduals. Then, as turbine energy changes, one of the wastegate and thescroll valve can be opened to manage boost response while using theother to manage exhaust pressure for residual control. Alternatively,one of the wastegate and the scroll valve may be opened initially, whilethe other is maintained closed. Then, as the turbine energy changessufficiently, the other which was closed may be opened, while the firstone is closed. An order of opening and closing may depend on therelative authority of each device at the various operating conditions.

In one example, an engine system comprises an engine, and a turbochargerfor providing a boosted aircharge to the engine, wherein theturbocharger includes an intake compressor and an exhaust turbine. Theexhaust turbine may include a first outer and a second inner scroll witha scroll valve coupled to an inlet of the first outer scroll but not toan inlet of the second inner scroll. A wastegate may be included in abypass coupled between an inlet and an outlet of the turbine. A firstEGR passage may be coupled between an engine exhaust, downstream of theturbine, and an engine intake, upstream of the compressor, the first EGRpassage including a first EGR valve. A second EGR passage may be coupledbetween the engine exhaust, upstream of the turbine, and the engineintake, downstream of the compressor, the second EGR passage including asecond EGR valve. The engine system may further include a controllerwith computer readable instructions for, opening one or more of thefirst EGR valve and the second EGR valve to provide engine dilution, andupon reaching a limit, providing further engine dilution by decreasingan opening of the scroll valve. The limit may include one of an openinglimit of the first EGR valve and/or an opening limit of the second EGRvalve. The controller may be configured to maintain the first and/orsecond EGR valve open while increasing the opening of the scroll valve.Alternatively, the controller may be configured to decrease the openingof the first and/or second EGR valve while increasing the opening of thescroll valve. The controller may be further configured to adjust theopening of each of the first and second EGR valve while decreasing theopening of the scroll valve to vary a ratio of high-pressure EGR tolow-pressure EGR delivered to the engine.

In another example, a method for an engine may include recirculatingresiduals from an engine exhaust to an engine intake via an EGR systemuntil a combustion stability is reached, and after the limit, reducinginternal residuals by moving a scroll valve coupled to an outer scrollof a multi-scroll turbine to a more open position. The method furtherincludes, while moving the scroll to the more open position, reducing anopening of a first LP-EGR valve and/or a second HP-EGR valve.

An example adjustment is now described with reference to FIG. 15. Map1500 of FIG. 15 depicts adjusting of a scroll valve coupled to an inletof an outer scroll of a multi-scroll exhaust turbine responsive toengine dilution. Map 1500 depicts an engine dilution requested at plot1501 (dashed line) and an engine dilution provided at plot 1502 (solidline). Map 1500 further depicts EGR valve adjustments at plot 1504 andscroll valve adjustments at plot 1506. All plots are depicted over time,plotted along the x-axis.

Prior to t1, the engine may be operating with the scroll valve (plot1506) at a more open position (e.g., at a fully open position). Further,the EGR valve (plot 1504) may be at a position that is based on theengine dilution needed (plot 1501) so that the requested engine dilutionis provided (plot 1502). As such, the engine dilution request mayinclude one or more of a low-pressure EGR request and a high-pressureEGR request. In one example, the engine dilution request may alsoinclude a ratio of LP-EGR to HP-EGR. In still another example, theengine dilution request may also include a ratio of internal EGR toexternal EGR.

At t1, based on a change in engine operating conditions, there may be anincreased request for engine dilution. For example, there may be anincreased demand for LP-EGR and/or HP-EGR. As such, the engine dilutionneeded may be within an engine combustion stability limit 1503.Accordingly, an opening of the EGR valve may be increased at t1, whilemaintaining a position of the scroll valve, to meet the increased enginedilution need. Increasing an opening of the EGR valve may includeincreasing an opening of a LP-EGR valve when the engine dilution requestincludes a request for more LP-EGR. Alternatively, the increasing mayinclude increasing an opening of a HP-EGR valve when the engine dilutionrequest includes a request for more HP-EGR. Further still, while plot1504 shows a single EGR valve, the opening of the EGR valve may includeopening of each of a LP-EGR valve and a HP-EGR valve to vary a ratio ofLP-EGR and HP-EGR provided based on the engine dilution request. Then,at t2, when the engine dilution request decreases, the EGR valve openingmay be correspondingly decreased.

At t3, based on a change in engine operating conditions, there may againbe an increased request for engine dilution. However, to provide thedesired engine dilution, at t3, the EGR valve may need to be openedbeyond its opening limit 1505. Since this is not possible, the EGR valvemay be fully opened and maintained at its opening limit 1505 and theremaining engine dilution need may be met by decreasing an opening ofthe scroll valve at t3. As such, by closing the scroll valve and usingscroll valve adjustments to provide the desired dilution, enginecombustion stability limits may be met, thereby improving engineperformance. Then, at t4, when the engine dilution request decreases,the EGR valve opening may be decreased and the scroll valve opening maybe correspondingly increased.

Herein, adjusting the scroll valve responsive to engine dilutionincludes adjusting the scroll valve responsive to an EGR request, theEGR request including one or more of LP-EGR, HP-EGR, or a ratio ofLP-EGR to HP-EGR, the ratio based on the requested engine dilution.Further still, the scroll valve opening may be adjusted responsive to aratio of internal EGR to external EGR, the ratio based on the requestedengine dilution.

As used herein, the adjusting responsive to engine dilution includesadjusting responsive to the engine dilution request relative to theengine combustion stability limit. For example, the scroll valve may bemoved to a more closed position as a request for engine dilutionincreases while the scroll valve is moved to a more open position as arequest for engine dilution decreases.

While the depicted example suggests closing the scroll valve, inalternate examples, the scroll valve may be opened in response to theengine dilution, the adjustment (opening or closing) based not only onthe engine dilution request but also on the engine EGR systemconfiguration. In one example, wherein the engine includes an EGR systemconfigured to recirculate exhaust gas from an engine exhaust to anengine intake, the adjusting may include, in response to an enginedilution request being higher than an engine dilution that can beprovided by the EGR system, increasing an opening of the scroll valve,and in response to the engine dilution request being lower than theengine dilution that can be provided by the EGR system, decreasing theopening of the scroll valve. Herein, the EGR system may include one ormore of a low-pressure EGR system including a first EGR valve and ahigh-pressure EGR system including a second EGR valve, and wherein oneor more of the first EGR valve and the second EGR valve is adjustedbased on the engine dilution request and the scroll valve adjustment. Inanother example, the adjusting of the scroll valve responsive to enginedilution may include increasing engine dilution by increasing opening ofa valve coupled to the EGR system while increasing an opening of thescroll valve, the increasing based on each of an engine dilution requestand an opening limit of the EGR valve. The adjusting responsive toengine dilution may further include decreasing engine dilution bydecreasing opening of the valve coupled to the EGR system whiledecreasing the opening of the scroll valve, the decreasing based on eachof the engine dilution request and a closing limit of the EGR valve.

In engine systems configured with an LP-EGR system, the scroll valve canbe positioned to provide the turbine power required to deliver the airand external EGR to the engine. At low engine loads, the turbine poweris higher with the scroll valve closed due to higher exhaust manifoldpressure. At some higher engine loads (system dependent), the openscroll valve may produce more turbine power due to increased mass flow.

In the depicted embodiment, cylinder valve timing may be maintainedduring the increasing and decreasing opening of the scroll valve.However, in alternate embodiments, valve timing adjustments may beconcurrently used alongside scroll valve adjustments to also meet theengine dilution. For example, valve timing may be adjusted to reducevalve overlap while the scroll valve opening is increased.

While not depicted in the example of FIG. 15, in further examples, acontroller may adjust a wastegate coupled across the exhaust turbineresponsive to the engine dilution, the wastegate adjusted based on thescroll valve adjustment and the engine dilution. The controller may alsoadjust various engine torque actuators, such as one or more of sparkignition timing, VCT, and intake throttle position based on the scrollvalve adjustment and the engine dilution.

In this way, scroll valve adjustments may be performed responsive toengine dilution. By closing the scroll valve when EGR valve limits arereached, or opening the scroll valve when engine combustion stability islimited, an amount of residuals delivered to the engine can be managedand engine dilution can be provided without degrading engineperformance.

Now turning to FIG. 9, an example routine 900 is shown for adjusting ascroll valve coupled to an inlet of an outer scroll of a multi-scrollexhaust turbine in response to an indication of pre-ignition to reduceengine load and mitigate engine damage. The routine allows enginehardware to be protected from pre-ignition and other hardware limits.

At 902, the routine includes estimating and/or measuring engineoperating conditions such as engine coolant temperature, exhaustcatalyst temperature, torque demand, BP, MAP, MAF, etc. In addition, aninitial scroll valve position may be determined based on the estimatedoperating conditions.

At 904, it may be determined if there is an indication of knock (withoutpre-ignition). If there is no indication of knock, then at 906, it maybe determined if there is an indication of pre-ignition. As such, at 904and 906, engine knock and pre-ignition may be identified anddistinguished from one another. If neither knock nor pre-ignition isdetermined at 904 and 906, the routine proceeds to 926 wherein thescroll valve is moved to the initial position, as determined andscheduled at 902. Further, at 928, a position of a wastegate coupledacross the exhaust turbine may be adjusted based on the scheduled scrollvalve position and further based on the engine operating conditions sothat a desired boost can be provided. Further still, the position of anEGR valve of the EGR system (including a LP-EGR valve of the LP-EGRsystem and an HP-EGR valve of the HP-EGR system) may be adjusted basedon the scheduled scroll valve position, the wastegate position, and theengine operating conditions to provide a desired engine dilution.

In one example, the indication of knock and the indication ofpre-ignition may be identified and distinguished based on the output ofa knock sensor coupled to the engine block. Based on a comparison of theoutput relative to a threshold, and further based on a timing (e.g., incrank angle degrees) of the output, a knock or pre-ignition event may bedetermined. As such, engine knock may be due to an abnormal combustionevent occurring in a cylinder after a spark ignition event of thecylinder while engine pre-ignition may be due to an abnormal combustionevent occurring in the cylinder before a spark ignition event of thecylinder. As an example, the indication of pre-ignition at 906 mayinclude a knock sensor output that is higher than a threshold and thatis received before a cylinder ignition event. In comparison, theindication of knock at 904 may include a knock sensor output that ishigher than the threshold and that is received after the cylinderignition event. In still another example, the knock sensor output may becompared to different thresholds for identifying knock and pre-ignition.For example, the indication of knock may be based on a knock sensoroutput that is higher than a first threshold received in a first windowwhile the indication of pre-ignition is based on a knock sensor outputthat is higher than a second threshold and that is received in a secondwindow, the second threshold higher than the first threshold, and thesecond window earlier than the first window. That is, pre-ignition mayresult in an earlier and relatively stronger vibration, received in thecylinder before the spark event, while knock may result in a later andrelatively softer vibration, received in the cylinder after the sparkevent.

In still further examples, the indication of pre-ignition may be basedon the output of one or more of a knock sensor, a torque sensor, and acrank acceleration sensor. Further still, the indication of knock orpre-ignition may include an indication regarding the likelihood of knockor pre-ignition. For example, based on engine operating conditions andfurther based on engine knock or pre-ignition history, it may beinferred whether pre-ignition or knock is likely and the routine of FIG.9 may be executed in response to the likelihood of knock or pre-ignitionbeing higher than a threshold.

At 904, in response to the indication of knock without pre-ignition, theroutine includes increasing an opening of the scroll valve to a lessopen position (that is, more open that the initial position butrelatively more closed relative to an opening used in response topre-ignition) so to reduce exhaust manifold pressure and internalresiduals. The adjusting in response to the indication of knock may bebased on a measurement of knock intensity from a knock sensor,in-cylinder pressure measurements or other means with an opening of thescroll valve increased as the knock intensity increases. At 910, theroutine includes further adjusting one or more of VCT, throttleposition, spark timing, cylinder fueling and EGR delivered to theknock-affected cylinder, while adjusting the scroll valve, the adjustingbased on the scroll valve adjustment. As such, these may includeactuator adjustments used to address knock. For example, in response tothe indication of knock, spark timing may be retarded, with the amountof spark retard applied adjusted based on the opening of the scrollvalve. Thus, as the scroll valve opening is increased in response toknock, an amount of spark retard that needs to be applied to address theknock may be decreased. By using the scroll valve to address the knock,the amount of spark retard required is decreased, thereby enabling knockmitigation with reduced fuel loss and improved fuel economy.

Further still, a wastegate coupled across the exhaust turbine may beadjusted based on the scroll valve adjustment. For example, as thescroll valve is moved to a more open position, the wastegate may also bemoved to a more open position. This further assists in reducingresiduals and in-cylinder temperature to mitigate the knock.

At 912, it may be determined if knock has been mitigated. For example,it may be determined if the indication of knock is less than thethreshold. If yes, the routine may proceed to 914 to resume the initialsettings, including the initial position of the scroll valve.Alternatively, engine actuator settings and scroll valve settings may bere-adjusted based on the prevalent engine operating conditions followingthe mitigation of knock. If knock has not been sufficiently mitigated at912, then at 916, the routine includes maintaining the scroll valveposition. For example, the controller may maintain the scroll valve atthe more open position for a duration until an in-cylinder temperatureis below a threshold, and then move the scroll valve to a more closedposition if desired.

Returning to 906, in response to the indication of pre-ignition, at 918,the routine includes adjusting the scroll valve to a more open positionto reduce engine load. The opening of the scroll valve responsive to theindication of pre-ignition is more than the opening responsive to theindication or knock. In one example, adjusting the scroll valve to themore open position includes fully opening the scroll valve.Alternatively, the scroll valve may be opened in discrete increments(e.g., in step-wise increments of 20%). By opening the scroll valve inresponse to the indication of pre-ignition, exhaust manifold pressurecan be reduced, thereby reducing an amount of trapped residuals in thecylinder that can contribute to further pre-ignition events. In oneexample, by opening the scroll valve in response to pre-ignition, engineload can be lowered from an elevated 17.5 bar level to a safer and morestable 16 bar load level within 1-2 seconds.

In one example, the adjusting of the scroll valve in response to theindication of pre-ignition may be based on exhaust manifold pressurewith an opening of the scroll valve increased as the exhaust manifoldpressure exceeds a threshold pressure. In another example, the adjustingof the scroll valve in response to the indication of pre-ignition may bebased on a turbine inlet temperature with an opening of the scroll valveincreased as the turbine inlet temperature exceeds a thresholdtemperature. For example, if the turbine inlet temperature is determinedto be beyond a threshold temperature corresponding to a materialdurability limit for more than a specified duration (e.g., at or above950° C. for more than 0.3 seconds), the scroll valve may be at leastpartially opened in order to rapidly reduce engine load to a safer levelwhere engine hardware will not be degraded.

As such, the threshold temperature at which the turbine inlet is limitedmay vary at different scroll openings. For example, the thermal stressesmay be higher when the scroll valve is fully closed. Accordingly, alower temperature threshold may be applied (e.g., 850° C.) when thescroll valve is closed while a higher temperature threshold is applied(e.g., 950-1000° C.) when the scroll valve is open.

In a further example, the adjusting of the scroll valve in response tothe indication of pre-ignition may be based on the intensity orfrequency of the pre-ignition, an opening of the scroll valve increasedas the intensity or frequency of pre-ignition increases. In yet anotherexample, the adjusting of the scroll valve in response to the indicationof pre-ignition may be based on engine speed with the opening of thescroll valve increased as the engine speed decreases. Further still, theadjusting of the scroll valve in response to the indication ofpre-ignition may be based on an air temperature including an ambient airtemperature or a manifold air temperature, the opening of the scrollvalve increased as the air temperature increases. In still anotherexample, the adjusting of the scroll valve in response to the indicationof pre-ignition may be based on one or more of ambient humidity and fueloctane content, the opening of the scroll valve increased as thehumidity decreases, the opening of the valve increased as the fueloctane content/rating decreases.

At 920, the routine includes further adjusting one or more of VCT,throttle position, spark timing, cylinder fueling and EGR delivered tothe knock-affected cylinder, while adjusting the scroll valve, theadjusting based on the scroll valve adjustment. As such, these mayinclude actuator adjustments used to address pre-ignition. For example,in response to the indication of knock, cylinder fuel injection may beenriched the cylinder, with the cylinder enrichment adjusted based onthe opening of the scroll valve. Thus, as the scroll valve opening isincreased in response to pre-ignition, an amount cylinder fuelenrichment that needs to be applied to address the pre-ignition may bedecreased. By using the scroll valve to address the pre-ignition, theamount of enrichment required is decreased, thereby enablingpre-ignition mitigation with reduced fuel loss and improved fueleconomy.

Further still, a wastegate coupled across the exhaust turbine may beadjusted based on the scroll valve adjustment. For example, as thescroll valve is moved to a more open position, the wastegate may also bemoved to a more open position. This further assists in reducing engineload, exhaust manifold pressure, and turbine inlet temperature tomitigate the pre-ignition.

It will be appreciated that there may be selected engine operatingconditions, such as selected engine speed-load conditions, wherein onlya wastegate adjustment can be used (in place of, and similar to a scrollvalve adjustment) to control the exhaust manifold pressure. For example,in response to the indication of pre-ignition, only a wastegateadjustment can be used to reduce exhaust manifold pressure and engineload to mitigate the pre-ignition. However, even if wastegateadjustments are possible, scroll valve adjustments may be advantageouseven in those operating conditions. As one example, scroll valveadjustments may enable the active controls of the wastegate to bedecoupled from the control of the scroll valve and the pre-ignitionmitigation. For example, based on control forces and valve authority(that is, based on authority of wastegate relative to scroll valve), oneor the other of the scroll valve and the wastegate may be selected forpre-ignition control. For example, during a first pre-ignitioncondition, where the wastegate has higher authority, the wastegate maybe opened to reduce engine load and mitigate the pre-ignition whileduring a second, different pre-ignition condition, where the scrollvalve has higher authority, the scroll valve may be opened to reduceengine load and mitigate the pre-ignition. During a third pre-ignitioncondition, where the wastegate and the scroll valve have substantiallysimilar authority, one of the two may be selected (e.g., the scrollvalve is opened while the wastegate is closed or the wastegate is openedwhile the scroll valve is closed). Alternatively, each of the scrollvalve and the wastegate may be at least partially opened to reduce theengine load. This provides less boost, lowers the engine load andmitigates the occurrence of pre-ignition.

At 922, it may be determined if pre-ignition has been mitigated andthere is no further indication of pre-ignition. For example, it may bedetermined if the turbine inlet temperature is less than a threshold.Alternatively, it may be determined if the exhaust manifold pressure isless than a threshold. If yes, the routine may proceed to 914 to resumethe initial settings, including the initial position of the scrollvalve. For example, the controller may open the scroll valve in responseto the indication of pre-ignition, maintain the scroll valve at the moreopen position for a duration until the exhaust manifold pressure isbelow a threshold, and after the exhaust manifold pressure has beenlowered and if there is no further indication of pre-ignition, move thescroll valve to a more closed position. Alternatively, engine actuatorsettings and scroll valve settings may be re-adjusted based on theprevalent engine operating conditions following the mitigation ofpre-ignition.

If pre-ignition has not been sufficiently mitigated at 922, then at 916,the routine includes maintaining the scroll valve position. For example,the controller may maintain the scroll valve at the more open positionfor a duration until the turbine inlet temperature, or the exhaustmanifold pressure, is below the respective threshold. Then, after thetemperature or pressure has been sufficiently lowered, the scroll valvemay be moved to a more closed position. For example, after the turbineinlet temperature is below the threshold temperature, the controller mayat least partially close the scroll valve, with the scroll valve closingbased on turbine speed or measured boost pressure. In one example, atleast partially closing the scroll valve includes moving the scrollvalve from the more open position to a fully closed position.

From 914 or 916, the routine proceeds to 924 where the routine includesadjusting one or more engine actuators during the scroll valvetransition to reduce any impact of a torque disturbance resulting fromthe scroll valve adjustment. For example, the routine may includeadjusting one or more of a wastegate coupled to the exhaust turbine,spark ignition timing, VCT, positive valve overlap, and intake throttleopening while moving the scroll valve to the more open position. Aselaborated with reference to FIG. 11, the actuator adjustment may beused to better mask any torque surge/dip that may arise during thescroll valve adjustment, thereby improving the vehicle operator's drivefeel. In one example, a timing of adjusting the scroll valve is based ona transmission event to reduce the torque impact.

In some embodiments, the scroll valve may be opened responsive to bothengine pre-ignition and knock, however the opening responsive topre-ignition may be more than the opening responsive to knock. Forexample, in response to the indication of pre-ignition, the scroll valvemay be adjusted to a first open position while in response to anindication of knock, the scroll valve is adjusted to a second openposition, the second position less open than the first position.

It will be appreciated that while the routine of FIG. 9 describes scrollvalve adjustments responsive to knock or pre-ignition, similar scrollvalve adjustments may be applied in response to other engine hardwarelimits being met or approached. For example, scroll valve adjustmentsmay be used in response to a turbine inlet temperature (e.g., asestimated by a thermocouple) approaching a limit determined by thematerial of the turbine, an exhaust valve temperature approaching alimit determined by the material of the exhaust valve, a peak cylinderpressure (e.g., as estimated by a cylinder pressure transducer)approaching a limit determined by the combination of temperature andmaterial of the exhaust valve, or a turbocharger speed (e.g., asestimated by a proximity sensor) approaching a limit. As such, eachparameter may be estimated or inferred based on a model. In each case,when the limit is met or approached, the scroll valve may be adjusted ina direction that reduces engine load, thereby reducing engine damage.Further, wastegate adjustments may be coordinated with the scroll valveadjustment to reduce degradation of the engine, turbocharger, andcatalyst.

In one example, an engine system comprises an engine and a turbochargerfor providing a boosted aircharge to the engine, the turbochargerincluding an intake compressor and an exhaust turbine. The exhaustturbine may include a first outer and a second inner scroll and a scrollvalve may be coupled between an engine exhaust manifold and an inlet ofthe first outer scroll, but not the inner scroll. A wastegate may beincluded in a bypass coupled between an inlet and an outlet of theturbine. A knock sensor may be coupled to the engine for identifying anddifferentiating cylinder knock and cylinder pre-ignition. An enginecontroller may be configured with computer readable instructions forindicating cylinder pre-ignition based on an output of the knock sensor,and in response to the indication of pre-ignition, the controller mayincrease an opening of the scroll valve based on turbine inlettemperature. The increasing may include, as the turbine inlettemperature exceeds a threshold, increasing an opening of the scrollvalve towards a fully open position, and as the turbine inlettemperature falls below the threshold, decreasing the opening of thescroll valve towards a fully closed position. Further, the controllermay adjust an opening of the wastegate based on the opening of thescroll valve, the wastegate moved to a more open position as the openingof the scroll valve is increased.

In this way, scroll valve adjustments may be advantageously used torapidly reduce engine load in response to engine hardware limits beingreached. By opening the scroll valve and optionally a wastegate inresponse to an indication of pre-ignition (such an indication regardinga likelihood of pre-ignition), exhaust manifold pressures and turbineinlet temperatures can be quickly decreased, reducing the risk ofimminent pre-ignition and engine damage.

An example adjustment is now described with reference to FIG. 13. Map1300 of FIG. 13 depicts adjusting of a scroll valve coupled to an inletof an outer scroll of a multi-scroll exhaust turbine responsive toengine hardware limit (specifically, in response to knock andpre-ignition in the present example). Map 1300 depicts a knock sensoroutput at plot 1302, scroll valve adjustments at plot 1304, and changesto an engine load at plot 1306. All plots are depicted over time,plotted along the x-axis.

Prior to t1, the engine may be operating with the scroll valve (plot1304) at a more closed position (e.g., at a fully closed position). Att1, in response to an engine knock sensor output (plot 1302) beinghigher than a first threshold Thr1 but lower than a second thresholdThr2, knock may be determined. In response to the indication of engineknock, the scroll valve may be moved to a more open position and may bemaintained in the more open position for a duration until the indicationof knock is below the first threshold. After the duration has elapsedand the indication of knock is below the first threshold, the scrollvalve may be returned to the more closed position. As such, by openingthe scroll valve in response to knock, the engine load may be reduced.In addition to the scroll valve adjustment, the engine knock may bemitigated by retarding spark timing (not shown).

Between t1 and t2, engine speed-load conditions may change and theengine may be operating at high engine load conditions where knock islikely. At t2, in response to the engine knock sensor output again beinghigher than the first threshold Thr1 but lower than a second thresholdThr2, knock may be determined. The indication of knock at t2 may behigher than the indication of knock at t1. In response to the indicationof engine knock at t2, the scroll valve may be moved to a more openposition (e.g., the same more open position as in response to theindication of knock at t1) and may be maintained in the more openposition for a duration until the indication of knock is below the firstthreshold. Herein, due to the indication of knock at t2 being higherthan the corresponding indication at t1, the scroll valve may be keptopen for a longer duration. Then, after the duration has elapsed, thescroll valve may be returned to the more closed position. In addition tothe scroll valve adjustment, the engine knock may be mitigated byretarding spark timing (not shown).

Between t2 and t3, engine speed-load conditions may change and theengine may be operating at low speed and high engine load conditionswhere pre-ignition is likely. At t3, in response to the engine knocksensor output (plot 1302) being higher than each of the first thresholdThr1 and second threshold Thr2, pre-ignition may be determined. Inresponse to the indication of engine pre-ignition, the scroll valve maybe moved to a more open position and may be maintained in the more openposition for a duration until the indication of pre-ignition is beloweach of the first and second threshold. Specifically, an opening of thescroll valve responsive to the indication of pre-ignition may be higher(that is, more open) than the opening of the scroll valve responsive tothe indication of knock. For example, in response to knock, the scrollvalve may be partially opened while in response to pre-ignition, thescroll valve may be fully opened. Further, the duration for which thescroll valve is opened responsive to the indication of pre-ignition maybe longer than the duration of scroll valve opening responsive to theindication of knock. For example, in response to knock, the scroll valvemay be opened until the indication of knock has reduced and then thevalve may be closed. In comparison, in response to pre-ignition, thescroll valve may be maintained open for a while even after theindication of pre-ignition has reduced, as shown.

After the longer duration has elapsed and the indication of pre-ignitionis below each of the first and second threshold, the scroll valve may bereturned to the more closed position. As such, by opening the scrollvalve in response to pre-ignition, the engine load may be quicklyreduced from the higher load region to a medium-low load region. Indoing so, the likelihood of further pre-ignition events is reduced. Inaddition to the scroll valve adjustment, the pre-ignition may bemitigated by enriching cylinder fuel injection for the duration (notshown).

While not depicted in the example of FIG. 13, in further examples, acontroller may adjust a wastegate coupled across the exhaust turbineresponsive to the indication of pre-ignition or knock, the wastegateadjusted based at least on the scroll valve adjustment. The controllermay also adjust various engine torque actuators, such as one or more ofspark ignition timing, VCT, EGR (LP-EGR and/or HP-EGR), and intakethrottle position based on the scroll valve adjustment.

In this way, scroll valve adjustments may be performed responsive toengine hardware limits being met or approached. By opening the scrollvalve to immediately reduce an engine load, engine components may beprotected from degradation and engine life may be extended.

Now turning to FIG. 10, an example routine 1000 is shown for adjusting ascroll valve coupled to an inlet of an outer scroll of a multi-scrollexhaust turbine in response to an indication of engine deactivation. Theadjustment enables turbine response during a subsequent tip-in to beimproved. By closing the scroll valve and wastegate during DFSO, theturbine speed is maximized and the actuators are pre-positioned for besttransient response on tip-in. Because the fuel is off, the increase inexhaust manifold pressure does not result in higher fuel consumption

At 1002, the routine includes estimating and/or measuring engineoperating conditions such as engine coolant temperature, exhaustcatalyst temperature, torque demand, BP, MAP, MAF, etc. In addition, aninitial scroll valve position may be determined based on the estimatedoperating conditions. At 1004, an indication of engine deactivation maybe confirmed. In the depicted example, the indication of enginedeactivation includes a deceleration fuel shut-off event (DFSO). TheDFSO event may be in response to torque demand being lower than athreshold, such as during a tip-out. Therein, cylinder fuel injectionmay be selectively stopped. In an alternate example, where the engine isconfigured to be selectively deactivated in response to idle-stopconditions, engine deactivation may be confirmed in response to anidle-stop operation being performed where cylinder fuel injection isdeactivated while spark is also deactivated. As such, following enginedeactivation, the engine may still be rotating, the vehicle may still betraveling, and the torque demand at the vehicle wheels may be negative.Further, the engine may spin towards rest un-fueled.

If engine deactivation is not confirmed, the routine proceeds to 1016wherein the scroll valve is moved to the initial position, as determinedand scheduled at 1002. Further, at 1018, a position of a wastegatecoupled across the exhaust turbine may be adjusted based on thescheduled scroll valve position and further based on the engineoperating conditions so that a desired turbine and/or engine speeddeceleration profile can be provided. Further still, the position of anEGR valve of the EGR system (including a LP-EGR valve of the LP-EGRsystem and an HP-EGR valve of the HP-EGR system) may be adjusted basedon the scheduled scroll valve position, the wastegate position, and theengine operating conditions to provide a desired engine decelerationprofile.

If engine deactivation is confirmed, then at 1006, the routine includesin response to the indication of engine deactivation, moving the scrollvalve to a more closed position. For example, the scroll valve may bemoved to a fully closed position. As such, the scroll valve may becoupled to only a first, outer scroll of the multi-scroll exhaustturbine but not to a second inner scroll of the turbine. In one example,the valve may be moved to the more closed position based on one or moreof turbine speed and boost pressure during the engine deactivation.Specifically, the valve may be moved based on a difference between anestimated or measured turbine speed during the engine deactivationrelative to a desired turbine speed deceleration profile and/or thedifference between a measured or estimated boost pressure relative to adesired boost pressure, the valve moved to a more closed position (e.g.,towards the fully closed position) as the difference increases. Thedesired turbine speed deceleration profile may allow the turbine speedto be maintained above a threshold level for a duration of the enginespin-down. By maintaining the turbine speed, exhaust manifold pressurecan be maintained elevated during the spin-down. The increased exhaustmanifold pressure reduces the air flow through the engine during thedeceleration, thereby reducing exhaust catalyst cooling. As such, thisreduces an amount of fuel enrichment required during a subsequent engineoperation to reactivate the exhaust catalyst, providing fuel economyimprovements.

At 1008, the routine further includes moving a wastegate coupled acrossthe exhaust turbine to a more closed position, the position of thewastegate based on the position of the scroll valve. Moving thewastegate may include moving the wastegate concurrently with the scrollvalve or sequentially with the scroll valve, an order of the sequentialmoving based at least on a relative authority of the wastegate and thescroll valve under the given engine operating conditions. For example,during a first condition where both the scroll valve and the wastegatehave comparable authorities, the controller may move the wastegate to amore closed position as the scroll valve is moved to the more closedposition. During a second condition, where the scroll valve has higherauthority, the controller may move the wastegate to the more closedposition after the valve is moved to the more closed position. During athird condition, where the wastegate has higher authority, the routineincludes moving the wastegate to the more closed position before thescroll valve is moved to the more closed position.

In addition, at 1008, the routine may include adjusting one or more ofVCT, valve timing, EGR, and an intake throttle position during theengine deactivation based on the moving of the scroll valve. Forexample, the controller may adjust intake and exhaust valve timingduring the deceleration to decrease valve overlap. The controller mayalso adjust the EGR valves to reduce an amount of residuals delivered tothe engine intake during the deceleration. The engine settings may beadjusted to maximize engine torque response after exit from DFSO. Thesemay include reducing or stopping EGR, and moving VCT to a timing foroptimum combustion stability with scroll valve closed.

At 1010, it may be determined if the turbine speed is below a thresholdspeed. During a DFSO, the scroll valve and wastegate may be closed tomaximize turbocharger response on exit from DFSO. In alternateembodiments, it may be determined if the engine speed is below athreshold speed. For example, it may be determined if the engine hasspun substantially to rest. If the turbine speed has not reduced belowthe threshold, then at 1011, the routine includes maintaining the scrollvalve in the closed position or continuously adjusting the scroll valveposition until the turbine speed has reduced according to the desireddeceleration profile.

As an example, as a difference between an estimated or measured turbinespeed and a desired spin-down turbine speed profile increases, theclosing of the scroll valve towards a fully closed position may beincreased (that is, the valve may be moved to a more closed position). Aclosing of the wastegate may be coordinated during the engine spin-downbased on the closing of the scroll valve to further reduce thedifference between the estimated or measured turbine speed and thedesired spin-down turbine speed profile. Likewise, where the enginesystem include an EGR system for recirculating exhaust gas from theexhaust manifold to an intake manifold of the engine, the controller mayfurther adjust an EGR valve of the EGR system to decrease an amount ofEGR during the closing of the scroll valve (and/or the wastegate). Inaddition cam timing will be adjusted for optimum combustion stability,this lowers fresh air flow through the unfueled cylinders therebyreducing exhaust catalyst cooling. As such, adjusting VCT for lowervolumetric efficiency may also reduce catalyst cooling, but EGR may nothave that effect because the EGR is fresh air when in DFSO. Further, byenabling the turbine speed to be maintained above a threshold speed fora duration of the engine deactivation (and spin-down), turbine spin-upduring a subsequent engine activation can be expedited, enabling betterboost control.

If the turbine speed has reduced below the threshold speed, then at1012, an initial scroll valve position may be resumed. Alternatively, adefault engine rest or DFSO scroll valve position may be resumed. In oneexample, this includes moving the scroll valve to a fully closedposition (if it has not already reached that position). Alternatively,if the scroll valve is already at the fully closed position, the routineincludes maintaining the scroll valve at the fully closed position. Instill other examples, the scroll valve may be moved to a fully openposition, at least temporarily.

In one embodiment, the position resumed at 1012 may be based on theduration of the DFSO. For example, in response to DFSO conditions beingmet, while fuel is deactivated, a timer may be started. In the event ofa shorter DFSO, where the duration elapsed on the timer is less than athreshold amount of time, the controller may temporarily move the scrollvalve to a fully open position to clear out residuals from the cylinder,and then return the scroll valve to the fully closed position. During asubsequent engine restart, the engine may be started with the scrollvalve closed to improve boost response (such as responsive to a tip-in,as elaborated in the routine of FIG. 7). In the event of a longer DFSO,where the duration elapsed on the timer is more than a threshold amountof time, the controller may maintain the scroll valve at a fully closedposition so that the turbine is maintained at a speed range from wherethe turbine can be quickly spun-up during a subsequent engine start. Forexample, during a first engine restart from the engine spin-down, acontroller may restart the engine with the scroll valve closed whileduring a second engine restart from the spin-down, the controller mayrestart the engine with the scroll valve open. Herein, a duration ofengine deactivation preceding the first engine restart may be longerthan the duration of engine deactivation preceding the second enginerestart. This allows boost response during the engine restart to beimproved.

At 1014, the routine includes adjusting one or more engine actuatorsduring the scroll valve transition to reduce any impact of a torquesurge/dip resulting from the scroll valve adjustment. For example, theroutine may include adjusting one or more of a wastegate coupled to theexhaust turbine, VCT, positive valve overlap, and intake throttleopening while moving the scroll valve to the more closed position. Aselaborated with reference to FIG. 11, the actuator adjustment may beused to better mask any torque disturbances that may arise during thescroll valve adjustment, thereby improving the vehicle operator's drivefeel. In one example, a timing of adjusting the scroll valve is based ona transmission event during the engine spin-down to better mask theimpact of a torque surge.

An example adjustment responsive to engine deactivation is now describedwith reference to FIG. 16. Map 1600 of FIG. 16 depicts adjusting of ascroll valve coupled to an inlet of an outer scroll of a multi-scrollexhaust turbine responsive to engine deactivation, specifically, inresponse to a DFSO event in the present example. Map 1600 depictsturbine speed at plot 1602, engine speed at plot 1604, cylinder fuelingat plot 1606, scroll valve adjustments at plot 1608, and wastegateadjustments at plot 1610. All plots are depicted over time, plottedalong the x-axis.

Prior to t1, the engine may be operating fueled (plot 1606) and each ofthe scroll valve and wastegate may be at a more open position. Forexample, each of the scroll valve and the wastegate may be at a fullyopen position. At t1, engine deactivation conditions may be met. Forexample, at t1, a vehicle operator may tip-out and/or apply wheelbrakes. In response to the reduced torque demand, fuel injection to theengine cylinders may be selectively deactivated. Due to thedeactivation, the engine may start spinning towards rest (plot 1604).

While the engine is spinning down, the scroll valve may be moved towardsa more closed position (e.g., towards a fully closed position). In thedepicted example, the scroll valve is shown being gradually moved to thefully closed position. However, in alternate examples, the scroll valvemay be immediately moved to a fully closed position, concurrent with thecylinder fuel deactivation. The closing of the scroll valve (plot 1608)may be adjusted based on turbine speed (plot 1602) so that a desiredturbine speed deceleration profile can be provided. As such, the desiredturbine speed deceleration profile enables the turbine speed to remainabove a threshold speed for a longer duration of the enginedeactivation. In other words, turbine spin-down to rest following enginedeactivation is slowed down. By keeping the turbine spinning, an exhaustmanifold pressure can be maintained, which in turns reduces air flowthrough the engine. The reduced air flow decreases cooling of theexhaust catalyst and depletion of catalytic sites with oxygen.

The scroll valve closing is gradually increased (as depicted, orimmediately decreased in an alternate example) after t1 until the scrollvalve is at a fully closed position, after which the scroll valve ismaintained at the fully closed position. In addition to scroll valveadjustments, wastegate adjustments may be used to assist in providingthe desired turbine speed deceleration profile. In the depicted example,the wastegate may also be closed in response to the engine deactivation,the closing of the wastegate following the closing of the scroll valve.Specifically, due to a higher authority of the scroll valve, the scrollvalve may start being moved towards a fully closed position at t1 whilethe wastegate may start being moved towards a fully closed positionshortly after t1 (after a delay since the moving of the scroll valvetowards the closed position). While the example shows the wastegatebeing gradually closed, in alternate examples, the wastegate may beimmediately closed. In still further examples, such as where thewastegate has higher authority, the wastegate may be immediately closedconcurrently with the immediate closing of the scroll valve and thedeactivating of fuel to the cylinders (e.g., at t1).

Just before t2, the engine may have spun to rest. In addition, each ofthe scroll valve and the wastegate may be at the fully closed position.At t2, engine reactivation conditions may be met. For example, thevehicle operator may tip-in and/or release wheel brakes. In response tothe increased torque demand, cylinder fueling may be resumed (plot1606). In addition, the scroll valve may be kept closed for a durationof the restart, between t2 and t3, until the turbine speed has beenraised above a threshold speed. By keeping the scroll valve closedduring an early part of the restart, turbine spin-up is expedited,reducing turbo lag and improving turbocharger performance upon restart.Then, at t3, the scroll valve may be gradually moved to a more openposition, for example, towards a fully open position.

The wastegate may also be kept closed during the early part of therestart to further assist in expediting turbine spin-up. Then, once theturbine has sufficiently spun up, the wastegate may be opened. In thedepicted example, the wastegate is kept closed during the enginerestart. Then, shortly after t3 (after a delay since the moving of thescroll valve towards the more open position), the wastegate is alsomoved towards the more open position.

As such, if the scroll valve was not closed during the enginedeactivation and maintained closed during at least a portion of thesubsequent engine reactivation, the turbine speed may drop faster duringthe engine deactivation and take a longer time to spin-up during thesubsequent engine reactivation, as shown by segment 1603 (dashed line).The delay in spinning up the turbine may result in turbo lag thatreduces turbocharger performance during the restart.

While the depicted example shows wastegate adjustments succeeding scrollvalve adjustments, in alternate embodiments, based on engine operatingconditions, wastegate adjustments may be concurrent with or may precedescroll valve adjustments. Further, while not depicted in the example ofFIG. 16, in other examples, a controller may adjust various enginetorque actuators, such as one or more of VCT, valve overlap, EGR andintake throttle position based on the scroll valve adjustment during theengine spin-down and the subsequent restart.

In this way, scroll valve adjustments may be performed responsive toengine deactivation conditions. By closing the scroll valve while theengine spins down, turbine speed may be better managed and turbochargercontrol may be improved.

Now turning to FIG. 11, an example routine 1100 is shown for adjusting atiming of a scroll valve adjustment based on an engine transmissionevent to reduce the impact, if any, of a torque surge associated withthe scroll valve adjustment. The routine allows such a torque surge tobe better masked, improving the quality of the vehicle operator's driveexperience.

At 1102, the routine includes determining the scroll valve adjustmentrequested. For example, the controller may determine whether the scrollvalve is to be moved to a more open position (e.g., to a fully openposition) or to a more closed position (e.g., to a fully closedposition). As previously elaborated, the engine may include a secondscroll inner to the first scroll, the scroll valve coupled only to thefirst scroll. The scroll valve adjustment may lead to transitioning of arestriction in exhaust upstream of the first scroll. As such, atransitioning of an opening of the scroll valve based on variousoperating conditions and operating limits leads to a transitioning in arestriction in exhaust upstream of a first scroll of a multi-scrollexhaust turbine based on various operating conditions and operatinglimits. These may include, for example, as elaborated with reference toFIGS. 5-10, cold-start conditions, engine dilution conditions,pre-ignition conditions, combustion stability limits, hardware limits,etc. Scroll valve adjustments may include, at lower turbine speeds,closing the scroll valve to increase restriction in exhaust upstream ofthe first scroll, and at higher turbine speeds, opening the scroll valveto decrease the restriction.

At 1104, a torque change associated with the scheduled scroll valveadjustment is determined. As such, the torque change may include atorque surge or a torque dip. For example, at moderate to high boostflow and airflow conditions, when the scroll valve is opened (atconstant cam timing), exhaust flow is allowed to go through bothscrolls. As a result the exhaust manifold pressure rapidly decreases,causing more fresh air to be trapped in the cylinders. If this increasein airflow is matched by fuel to maintain constant air-fuel ratio andignition timing, the opening of the scroll valve produces a “bump” up inengine torque, herein also referred to as a torque bump or torque surge.In a similar fashion, if the engine is at a moderate to high airflow,and the scroll valve is closed to help spool up the turbine, theelevated exhaust manifold pressure will cause the trapped aircharge tosuddenly decrease, while also reducing further fresh air flow into theengine. If this decrease in airflow is matched by fuel to maintainconstant air-fuel ratio and ignition timing, the closing of the scrollvalve produces a “bump” down in engine torque, herein also referred toas a torque bump or torque dip. In either case, the torque disturbance,or torque bump, leads to poor drivability. As elaborated below, anengine controller may be configured to adjust an engine actuator duringthe scroll valve transition to maintain engine torque and reduce theimpact of the torque bump.

At 1106, it may be determined if a torque bump is expected.Specifically, based on the estimation of a torque change associated withthe scheduled scroll valve adjustment, it may be determined if a torquesurge or torque dip is expected. In one example, a torque surge may beconfirmed if the torque change associated with the scheduled scrollvalve adjustment is a positive change that is more than a thresholdamount. In another example, a torque dip may be confirmed if the torquechange associated with the scheduled scroll valve adjustment is anegative change that is more than a threshold amount.

If a torque bump is not expected, then at 1108, the routine includesmaintaining the position of one or more engine actuators. Further, thescroll valve adjustment is performed as scheduled (e.g., at a timingbased on the estimated operating conditions).

If a torque bump is expected, then at 1110, it may be determined ifthere is an upcoming transmission event. The controller may determine ifthere is an upcoming transmission event based on the shift schedule ofthe transmission. The upcoming transmission event may include anupcoming transmission upshift event or an upcoming transmissiondownshift event. As such, the engine transmission may include a manualtransmission or an automatic transmission. The transmission may furtherinclude one or more clutches such as a torque converter clutch, and aforward clutch. The one or more clutches may include a mechanical clutchthat is mechanically actuated, as well as an “e-clutch” that iselectronically actuated (that is, a clutch-by-wire).

In some embodiments, in determining if there is an upcoming transmissionevent, the controller may determine a duration between the upcomingtransmission event (based on a shift schedule of the transmission) and atime when a request for transitioning restriction at the scroll valve isreceived. If the duration is sufficiently long (e.g., longer than athreshold duration), an upcoming transmission event may not beconfirmed. If the duration is sufficiently short (e.g., shorter than athreshold duration), an upcoming transmission event may be confirmed.

If an upcoming transmission event is confirmed, then at 1116, theroutine includes adjusting a timing of the transitioning based on atransmission event. The adjusting may include, in response to anupcoming transmission event, timing the transitioning to at leastpartially overlap the transmission event. For example, if a durationbetween the transmission event and a request for transitioningrestriction is smaller than a threshold, the timing of the scroll valvetransitioning may be adjusted to be during the transmission event (e.g.,concurrent with the transmission event). In another example, the timingmay be adjusted so that the timing of the transitioning immediatelyfollows the transmission event. By timing the transitioning to at leastpartially overlap the transmission event, the impact of the torque bumpcan be better masked, thereby improving driveability.

At 1118, the routine includes adjusting an engine actuator during thescroll valve transition to maintain engine torque and reduce the impactof a torque bump that would have been experienced during the transition.The engine actuator adjusted may include one or more of VCT, EGR, valvetiming (including adjusting a valve overlap), intake throttle position,wastegate, and transmission shift schedule. In each case, the engineactuator adjustment may be based on the transitioning of the scrollvalve opening and the change in restriction in exhaust upstream of thefirst scroll. For example, the engine actuator may be adjusted totransiently increase engine airflow when the scroll valve is closed toincrease restriction, and the engine actuator may be adjusted totransiently decrease engine airflow when the scroll valve is opened todecrease restriction. Alternatively, the engine actuator may be adjustedto increase engine airflow when the scroll valve is transitioned by alarge amount to a more open position or to a more closed position. Inthis way, a restriction in exhaust upstream of a first scroll of amulti-scroll exhaust turbine may be transitioned based on operatingconditions while adjusting an engine actuator during the transition tomaintain engine torque during the transition.

As another example, when closing the scroll valve to increaserestriction, an engine actuator may be adjusted to transiently increaseengine air flow. This transient increase in engine air flow maycompensate for the transient drop in air flow experienced when thescroll valve is closed and the exhaust manifold pressure is increased.As another example, when opening the scroll valve to decreaserestriction, the engine actuator may be adjusted to transiently decreaseengine air flow. This transient decrease in engine air flow maycompensate for the transient rise in air flow experienced when thescroll valve is opened and the exhaust manifold pressure is decreased.As one example, when the scroll valve is closed, the intake throttleopening may be temporarily increased to transiently increase the engineair flow while when the scroll valve is opened, the intake throttleopening may be temporarily decreased to transiently decrease the engineair flow.

As another example, when closing the scroll valve to increaserestriction, the engine actuator may be adjusted to decrease enginedilution, to compensate for higher internal residuals due to higherexhaust manifold pressure. In comparison, when opening the scroll valveto decrease restriction, the engine actuator may be adjusted to increaseengine dilution. As still another example, when timing the transitioningduring the transmission event, clutch slippage and/or spark retard maybe adjusted (e.g., increased) during the transitioning, the increasingbased on the transitioning. Therein, the amount of clutch slippage maybe increased as the transitioning of the scroll valve increases.Likewise, an amount of spark retard applied may be increased as thetransitioning of the scroll valve increases.

If an upcoming transmission event is not confirmed at 1110, for example,if the duration between the transmission event and the request fortransitioning restriction is larger than the threshold, at 1112, theroutine includes performing the scroll valve adjustment as scheduled.This may include timing the transitioning to be before any (subsequent)transmission event.

An example adjustment to the timing of a scroll valve transition isdescribed with reference to FIG. 12. Specifically, map 1200 of FIG. 12depicts a desired scroll valve schedule at plot 1202, a transmissionshift schedule at plot 1204, and an actual or commanded scroll valveschedule at plot 1206. Actuator adjustments (herein intake throttleadjustments) applied during the scroll valve transition are described atplot 1208. All plots are shown over time (along the x-axis).

Prior to t1, the engine may be operating with the scroll valve more open(plot 1206). For example, the scroll valve may be fully open. Based onengine operating conditions before t1, a controller may determine at t1that the scroll valve is to be transitioned to a more closed position(e.g., a fully closed position). For example, in response to an increasein torque demand, boost may need to be increased at or after t1.Accordingly, a scroll valve transition request (plot 1202) may be madeat t1. The controller may further determine that the scroll valveadjustment needs to be performed between t1 and t3. In other words, ifthe scroll valve adjustment is performed after t3, engine performancewill be degraded. The controller may further determine if there is anupcoming transmission event, such as where a transmission gear isengaged. Based on the engine operating conditions, it may be determinedthat a transmission upshift or gear engagement (plot 1204) is scheduledto start at t2. In view of the upcoming transmission event, the scrollvalve transition requested at t1 may be actually commanded shortly aftert2, specifically, during the transmission upshift or gear engagement. Inthe depicted example, the transmission upshift may be performed inmultiple upshift steps and the scroll valve closing may be transitionedto occur after the first upshift step has been completed.

As such, if a transmission event is not confirmed between t1 and t3,then the scroll valve transition commanded at t1 may be actuallyperformed at t1 (see dashed segment 1207). As another example, at t4,based on engine operating conditions, a request to open the scroll valvemay be made. Since no transmission events are expected soon after t4,the controller may command the requested scroll valve transition at t4.Thus, at t4, the scroll valve may be transitioned from the more closedposition to the more open position.

By timing a scroll valve transition to at least partially overlap thetransmission event (as occurs between t2 and t3), driveability isimproved. Further driveability improvements during scroll valvetransition are achieved by engine actuator adjustments that increaseengine airflow during the closing of the scroll valve. Specifically,closing of the scroll valve causes exhaust manifold pressure to rise,which in turn reduces fresh air flow into the cylinders for a few enginecycles following the closing of the scroll valve. Then, as the turbinespeed picks up due to the rise in exhaust manifold pressure, boost isincreased and fresh air flow to the engine cylinders increases. Thus, tocompensate for the torque dip resulting from the reduced airflow, uponreceiving the request for scroll valve closing and before the scrollvalve is closed, specifically between t1 and t2, the opening of anintake throttle may be increased. Then, during the first few cyclesfollowing the closing of the scroll valve, specifically between t2 andt3, the intake air throttle opening may be further increased (more thanthe opening between t1 and t2). For example, between t1 and t2, thethrottle may be partially open and between t2 and t3, the throttle maybe fully open. Then, as the turbine speed and boost level picks up,specifically after t3, the intake air throttle may resume its originalposition.

Likewise, engine actuator adjustments that decrease engine airflowduring the scroll valve transition at t4 may be used to improvedriveability during scroll valve opening. Specifically, opening of thescroll valve causes exhaust manifold pressure to drop, which in turnincreases fresh air flow into the cylinders for a few engine cyclesfollowing the opening of the scroll valve. Then, as the turbine speeddrops due to the drop in exhaust manifold pressure, boost is decreasedand fresh air flow to the engine cylinders decreases. Thus, tocompensate for the torque surge resulting from the increased airflow,during the first few cycles following the opening of the scroll valve,specifically immediately after t4, an intake air throttle may betemporarily opened. For example, the intake throttle opening may begradually increased (in the depicted example, stepwise increased). Then,as the turbine speed and boost level drops, the intake air throttle maybe resume its original position (that is, the opening of the intakethrottle may be increased).

Wastegate adjustments (not shown) may also be used during each of thescroll valve transitions to further assist in turbocharger control. Forexample, the wastegate may be opened when the scroll valve is opened andthe wastegate may be closed when the scroll valve is closed. In thisway, actuator adjustments may be used to improve driveability during ascroll valve transition.

In this way, a binary flow turbine may be advantageously used to improveboost control at various engine operating conditions. By adjusting thevalve during cold-start conditions, increased manifold pressure can beused to expedite catalyst warm-up as well as turbine spin-up during thecold-start. In addition, scroll valve adjustments may be used to bringturbine speed out of a speed range where audible resonance can occur,improving drive feel. By adjusting the valve responsive to transientchanges in torque demand, turbo lag can be reduced, improving theengine's boost response. Furthermore, by adjusting the valve responsiveto engine deactivation, turbine spin-up upon engine reactivation is alsoimproved. By adjusting the valve responsive to engine dilution,residuals can be delivered to the engine without degrading combustion,thereby extending the benefits of EGR to a wider range of operatingconditions. By adjusting the valve when engine hardware limits arereached, such as responsive to pre-ignition, engine load can be quicklylowered and component damage can be reduced. By using one or more engineactuators to compensate for the torque impact of the scroll valveadjustment, the torque impact felt by a vehicle operator is reduced. Inaddition, by adjusting the timing based on a transmission event, thetorque impact is better masked. Overall, engine performance and boostresponse is improved, exhaust emissions are reduced, and vehicledriveability is improved.

Note that the example control and estimation routines included hereincan be used with various engine and/or vehicle system configurations.The control methods and routines disclosed herein may be stored asexecutable instructions in non-transitory memory. The specific routinesdescribed herein may represent one or more of any number of processingstrategies such as event-driven, interrupt-driven, multi-tasking,multi-threading, and the like. As such, various actions, operations,and/or functions illustrated may be performed in the sequenceillustrated, in parallel, or in some cases omitted. Likewise, the orderof processing is not necessarily required to achieve the features andadvantages of the example embodiments described herein, but is providedfor ease of illustration and description. One or more of the illustratedactions, operations and/or functions may be repeatedly performeddepending on the particular strategy being used. Further, the describedactions, operations and/or functions may graphically represent code tobe programmed into non-transitory memory of the computer readablestorage medium in the engine control system.

It will be appreciated that the configurations and routines disclosedherein are exemplary in nature, and that these specific embodiments arenot to be considered in a limiting sense, because numerous variationsare possible. For example, the above technology can be applied to V-6,I-4, I-6, V-12, opposed 4, and other engine types. The subject matter ofthe present disclosure includes all novel and non-obvious combinationsand sub-combinations of the various systems and configurations, andother features, functions, and/or properties disclosed herein.

The following claims particularly point out certain combinations andsub-combinations regarded as novel and non-obvious. These claims mayrefer to “an” element or “a first” element or the equivalent thereof.Such claims should be understood to include incorporation of one or moresuch elements, neither requiring nor excluding two or more suchelements. Other combinations and sub-combinations of the disclosedfeatures, functions, elements, and/or properties may be claimed throughamendment of the present claims or through presentation of new claims inthis or a related application. Such claims, whether broader, narrower,equal, or different in scope to the original claims, also are regardedas included within the subject matter of the present disclosure.

1. A method for an engine, comprising: adjusting a scroll valve coupledto an inlet of one scroll of a multi-scroll exhaust turbine responsiveto an indication of engine deactivation.
 2. The method of claim 1,wherein the indication of engine deactivation includes a decelerationfuel shut-off.
 3. The method of claim 1, wherein the one scroll is afirst, outer scroll, the multi-scroll exhaust turbine including asecond, inner scroll, the valve not coupled to an inlet of the secondscroll.
 4. The method of claim 1, wherein the adjusting includes, inresponse to the indication of engine deactivation, moving the scrollvalve to a more closed position.
 5. The method of claim 4, whereinmoving the scroll valve to the more closed position includes moving thescroll valve to the more closed position based on one or more of turbinespeed or boost pressure during the engine deactivation.
 6. The method ofclaim 5, wherein the moving based on turbine speed includes moving thescroll valve based on a difference between an estimated or measuredturbine speed during the engine deactivation relative to a turbine speeddeceleration profile and/or the difference between measured and desiredboost pressure, the scroll valve moved towards a fully closed positionas the difference increases.
 7. The method of claim 6, furthercomprising, moving a wastegate coupled across the exhaust turbine to amore closed position in response to the indication of enginedeactivation, the wastegate position based on the scroll valve position.8. The method of claim 7, wherein moving the wastegate includes, duringa first condition where the wastegate and scroll valve havesubstantially similar authority, moving the wastegate to the more closedposition as the scroll valve is moved to the more closed position;during a second condition where the scroll valve has higher authority,moving the wastegate to the more closed position after the scroll valveis moved to the more closed position; and during a third condition wherethe scroll valve has lower authority, moving the wastegate to the moreclosed position before the scroll valve is moved to the more closedposition.
 9. The method of claim 6, further comprising, adjusting one ormore of VCT, valve overlap, EGR, and intake throttle position during theengine deactivation based on the moving of the scroll valve.
 10. Themethod of claim 4, wherein a timing of moving the scroll valve to themore closed position is based on a transmission event.
 11. A method fora boosted engine, comprising: deactivating fuel injection to an engine;and while the engine spins towards rest, adjusting a scroll valvecoupled to an outer scroll of a multi-scroll exhaust turbine based ondeviation of estimated turbine speed relative to a turbine speeddeceleration profile.
 12. The method of claim 11, wherein deactivatingfuel injection to the engine includes deactivating in response to atip-out.
 13. The method of claim 11, wherein the adjusting includes, asthe deviation of the estimated or measured turbine speed from theturbine speed deceleration profile increases, moving the scroll valvetowards a fully closed position.
 14. The method of claim 11, wherein atiming of adjusting the scroll valve is based on a transmission eventduring the engine spin-down.
 15. The method of claim 13, furthercomprising, moving a wastegate coupled across the exhaust turbinetowards a more closed position while the engine spins towards rest, theposition of the wastegate based on the scroll valve position.
 16. Themethod of claim 15, further comprising, adjusting one or more of VCT,EGR, intake throttle position, and valve overlap while the engine spinstowards rest, the adjusting based on the scroll valve adjustment.
 17. Anengine system, comprising: an engine including selectively deactivatablefuel injectors; a turbocharger for providing a boosted aircharge to theengine, the turbocharger including an intake compressor and an exhaustturbine, the exhaust turbine including a first outer scroll and a secondinner scroll; a scroll valve coupled between an exhaust manifold of theengine and an inlet of the first outer scroll; a wastegate included in abypass coupled between an inlet and an outlet of the exhaust turbine;and a controller with computer readable instructions for, in response totorque demand being lower than a threshold, selectively deactivatingfuel injection to the engine; and while the engine spins down to rest,decreasing an opening of the scroll valve, the decreasing based on adifference between an estimated or measured turbine speed and a desiredspin-down turbine speed profile during the spin-down.
 18. The system ofclaim 17, wherein the controller includes further instructions forcoordinating an opening of the wastegate during the engine spin-downbased on the decreasing an opening of the scroll valve to further reducethe difference between the estimated or measured turbine speed and thedesired spin-down turbine speed profile.
 19. The system of claim 17,further comprising an EGR system configured to recirculate exhaust gasfrom the exhaust manifold to an intake manifold of the engine, whereinthe controller includes further instructions for adjusting an EGR valveof the EGR system to decrease an amount of EGR during the decreasing ofan opening of the scroll valve.
 20. The system of claim 17, wherein thecontroller includes further instructions for, during a first enginerestart from the spin-down, restarting the engine with the scroll valveclosed; and during a second engine restart from the spin-down,restarting the engine with the scroll valve open, a duration of enginedeactivation preceding the first engine restart longer than the durationof engine deactivation preceding the second engine restart.